Ryanair was legally incorporated on November 28, 1984, by three Irish businessmen - Tony Ryan, Christopher Ryan, and Liam Lonergan, with Tony Ryan's sons also playing key roles in the startup.

Originally established as Dawndell Limited on 30 May 1985, Ryanair UK was later renamed Ryan Air UK Limited on 27 June 1985, and finally became Ryanair UK Limited on 1 November 1995.

Ryanair's first flight took place on July 8, 1985, using a single Embraer EMB-110P1 Bandeirante aircraft, carrying just 15 passengers between Waterford, Ireland, and London-Gatwick Airport, UK.

In 1986, Ryanair expanded its fleet by acquiring two Rolls-Royce Dart-powered Hawker Siddeley HS 748s, allowing the airline to start a new high-frequency service between Dublin and Luton.

In 1987, Ryanair entered the jet age by leasing three BAC1-11 aircraft from TAROM Romanian Airlines, marking a significant milestone in the airline's fleet expansion.

In 1988, Michael O'Leary became the chief financial officer of Ryanair, marking a significant addition to the company's leadership team.

In 1991, Ryanair transitioned to a low-cost model by focusing on a single type of aircraft, the BAC 1-11, and eliminating all onboard food and drink services. This strategic shift led to the airline's first profitable year of operations.

The European Union's deregulation of the air industry in 1992 allowed carriers like Ryanair to operate scheduled services between EU states, leading to significant growth opportunities for the airline.

In 1993, Aer Lingus made a £25 million offer to acquire Ryanair, but Ryanair declined the offer. Instead, Ryanair surpassed both Aer Lingus and British Airways as the leading carrier on the Dublin-London route.

In 1995, Ryanair phased out its BAC 1-11 aircraft and introduced used Boeing 737-200s to modernize its fleet. The larger capacity of the Boeing planes allowed Ryanair to take full advantage of the liberalized air services policy in the EU.

Ryanair Holdings was established in 1996 as a holding company for Ryanair with the two companies having the same board of directors and executive officers.

The airline went public in 1997, and the money raised was used to expand the airline into a pan-European carrier.

In 1998, Ryanair placed a substantial order worth $2 billion for 45 new Boeing 737-800 series aircraft, signaling a major investment in expanding its fleet.

In January 2000, Ryanair launched its first website coinciding with the new millennium, embracing the trend of online sales in the emerging Worldwide Web. The move allowed customers to book air travel directly with the airline, eliminating the need for commissions to travel agents.

By 2002, Ryanair had firmly established itself with a significant increase in passengers year-on-year. The airline expanded its fleet by increasing the original order for Boeing 737-800s to 125 airplanes, with further options for more, leading to substantial growth in passenger numbers.

In April 2003, Ryanair acquired Buzz, its struggling competitor, from KLM, consolidating its position in the low-cost airline market.

In 2004, Michael O'Leary predicted a 'bloodbath' in the airline industry, with Ryanair and EasyJet expected to survive. Despite initial losses, Ryanair quickly returned to profitability.

By August 2005, Ryanair claimed to have carried 20% more passengers within Europe than British Airways, solidifying its position as one of the largest carriers on European routes.

A documentary aired on Channel 4's Dispatches series criticized Ryanair's training policies, security procedures, and aircraft hygiene, while highlighting poor staff morale. Ryanair denied the allegations and claimed that some promotional materials were fabricated.

For the six months ending on 30 September 2006, Ryanair experienced a substantial increase in passenger traffic and revenue, with over 22 million passengers and revenues of €1.256 billion.

Ryanair launched a bid of €1.48 billion to acquire Aer Lingus, but the offer was rejected by Aer Lingus on the same day, citing contradictions.

Ryanair announced plans to establish a new long-haul airline separate from its operations, offering low-cost and business class services to compete with airlines like Virgin Atlantic. The launch was delayed due to aircraft availability.

Ryanair changed its policy to charge passengers for airport check-in, aiming to reduce overhead costs.

On November 10, 2008, Ryanair Flight 4102 from Frankfurt–Hahn Airport to Ciampino–G. B. Pastine International Airport in Rome suffered multiple bird strikes during landing. The Boeing 737-8AS jet, with 172 people on board, including crew and passengers, experienced significant damage, leading to it being written off.

Ryanair launched a second bid to acquire Aer Lingus, offering €748 million in an all-cash offer. Despite the premium offer, Aer Lingus rejected the bid, leading to Ryanair walking away from the takeover.

In February 2009, Ryanair confirmed its plan to close all check-in desks by the start of 2010. Passengers would be able to leave their luggage at a bag drop, with all other check-in processes to be done online.

In a live BBC News interview on February 27, 2009, Ryanair's CEO Michael O'Leary mentioned the possibility of charging passengers £1 to use the toilet on flights as a publicity stunt. This controversial idea generated significant media attention for the airline.

On 5 September 2009, Ryanair reached a milestone as its fleet reached 200 aircraft for the first time. This marked a significant achievement for the airline.

In April 2010, following flight disruptions caused by the 2010 eruptions of Eyjafjallajökull in Iceland, Ryanair decided to comply with EU regulations and reimburse stranded passengers.

In July 2010, Ryanair faced controversy for circulating advertisements offering £10 one-way fares to European destinations, which were deemed 'likely to mislead' by the ASA following a complaint from EasyJet.

In August 2010, Ryanair held a press conference in Plovdiv and announced its first-ever Bulgarian destination connecting Plovdiv with London Stansted.

In the last three months of 2010, Ryanair made a loss of €10.3 million, attributing it to strikes, flight cancellations, and severe weather conditions.

On 4 April 2011, Ryanair began adding a surcharge of €2 to its flights to cover the costs arising from compliance with EC Regulation 261/2004, which requires it to pay for meals and accommodation for passengers on delayed and cancelled flights.

On 19 June 2012, Ryanair Chief Executive Michael O'Leary announced his intention to make an all-cash offer for Aer Lingus. The bid was later blocked by the European Commission in 2017.

On 26 July 2012, three Ryanair aircraft inbound to Madrid–Barajas Airport diverted to Valencia Airport due to severe thunderstorms in the Madrid area. The aircraft declared an emergency due to low fuel reserves after being held in the air for an extended period.

On 13 March 2013, Ryanair signed an order for 175 new Boeing 737-800s. This large order showcased the airline's commitment to expanding its fleet.

On 27 January 2014, Ryanair moved into a new €20m, 100,000 sq ft Dublin head office in Airside Business Park, officially opened on 3 April 2014.

On 16 April 2014, the Dutch Court ruled in favor of the Dutch investigative journalism programme KRO Reporter, stating that Ryanair's fuel policy was under scrutiny. The court found evidence supporting claims of pressure on pilots to carry minimal fuel to reduce costs.

On 30 April 2014, Ryanair confirmed the order of five more aircraft to add to its fleet. This expansion plan aimed to increase the number of aircraft in the airline's fleet.

On June 17, 2014, Ryanair launched a campaign to re-invent itself as a family-friendly airline, aiming to improve customer service and attract more families. The company's CEO emphasized the importance of catering to family travelers.

On 8 September 2014, Ryanair committed to ordering 100 new Boeing 737 MAX 8s, with options for an additional 100. This decision reflected the airline's strategy to modernize its fleet.

On 1 December 2014, Ryanair finalized its order for up to 200 Boeing 737 MAX 200s, becoming the launch customer for this version designed for low-cost airlines. This marked a significant milestone in the airline's fleet expansion.

In May 2015, the Mayor of Copenhagen announced a boycott of Ryanair following protests from Danish unions about employment conditions. Ryanair relocated its bases out of Denmark after a court upheld the unions' right to strike.

The airline confirmed plans to open an operating base at Milan Malpensa Airport in December 2015, initially with one aircraft.

On 9 March 2016, Ryanair launched a corporate jet charter service, offering a Boeing 737-700 for corporate or group hire.

In December 2017, Ryanair UK submitted an application to the Civil Aviation Authority for an air operator's certificate in preparation for a potential 'hard Brexit'.

On May 22, 2018, Ryanair's remarkable growth in profits, fleet size, and route expansion was highlighted in Airways magazine.

On 10 August 2018, pilots from Germany, Sweden, Ireland, Belgium, and the Netherlands staged a 24-hour strike, leading to the cancellation of 400 flights. This strike was one of the largest in Ryanair's history, primarily over pay issues.

On August 23, 2018, Ryanair announced a new baggage policy which included Priority Boarding allowing for larger and smaller bags. This policy aimed to simplify baggage rules and reduce turnaround times.

On 26 September 2018, Ryanair had to cancel 150 flights, about 6% of its total flights, due to strikes in several European countries. The British Civil Aviation Authority urged compensation for affected passengers under EU Regulation 261, but Ryanair refused to accept claims, leading to legal action.

On September 28, 2018, pilots, cabin crew, and other staff went on strike due to issues with employment contracts and pay. The strike led to the cancellation of 250 flights affecting around 40,000 passengers.

On January 3, 2019, Ryanair UK obtained an air operator's certificate from the Civil Aviation Authority and officially began operations on behalf of Ryanair on March 12, 2019.

On June 9, 2019, Ryanair announced the establishment of Malta Air in collaboration with the Government of Malta. The new airline took over Ryanair's operations in Malta with an initial fleet of ten aircraft.

During the A4E Aviation Summit in Brussels, Ryanair's CEO, Michael O'Leary, expressed his expectation of a recovery from the COVID-19 pandemic by the summer of 2020, despite initially underestimating its impact.

In response to the COVID-19 pandemic, Ryanair announced the loss of 3000 jobs, mainly affecting pilots and cabin crew, as part of operational changes due to the significant decrease in demand.

On March 10, 2021, Ryanair UK registered its second Boeing 737-800, previously operated by Buzz as SP-RKA and now registered as G-RUKB.

On 17 May 2021, Ryanair released its full financial report, revealing a record annual loss of $989 million, underscoring the unprecedented challenges encountered by the airline amidst the COVID-19 pandemic.

On 23 May 2021, Ryanair Flight 4978 en route from Athens to Vilnius was diverted to Minsk National Airport due to a false bomb threat. Belarusian authorities removed a journalist and opposition activist from the plane, leading to international condemnation and calls for investigation.

After delays due to the grounding of the 737 MAX, the first 737 MAX 200 was delivered to Ryanair on 16 June 2021. This marked the beginning of the airline's fleet renewal with the new aircraft model.

As of April 2022, Ryanair, the Irish low-cost carrier, operates flights to 229 year-round and seasonal destinations across 37 countries.

In June 2022, Ryanair faced backlash for requiring South Africans to take a general knowledge test in Afrikaans before boarding UK-bound flights. The decision was met with criticism due to the language's historical connotations in South Africa.

By October 2022, Ryanair UK had a total of eight aircraft based at Stansted and Manchester, showcasing the airline's growth and presence in the region.

In November 2022, Ryanair announced its plan to have 124 Boeing 737 MAX 200 aircraft by summer 2023, reducing the number of unfulfilled orders. This demonstrated the airline's continued growth and fleet expansion.

On 30 January 2023, Ryanair Holdings CFO Neil Sorahan announced the extension of A320 leases to 2028. This decision provided stability in the airline's fleet planning.

On 9 April 2023, Ryanair Flight 5542 flying from Liverpool to Dublin had an emergency landing resulting in front gear damage. The incident led to the temporary closure of the southern runway at Dublin Airport, with no injuries reported.

During a flight from Bologna to Tel Aviv on 10 June 2023, a Ryanair cabin crew member mistakenly announced that the flight would be landing in Palestine instead of Tel Aviv, causing upset among passengers. The airline issued an apology following the incident.

In January 2024, Ryanair announced its consideration of taking on Boeing 737 MAX 10 orders that might become available due to issues affecting Boeing's production line.

As of March 2024, the Ryanair UK fleet is composed of a specific number of aircraft.