The Royal Exchange was established in 1571 by English financier Thomas Gresham and Sir Richard Clough, following the model of the Antwerp Bourse. It was inaugurated by Queen Elizabeth I of England.

Following the destruction of Gresham's Royal Exchange building in the Great Fire of London, it was reconstructed and re-established in 1669. This marked a shift away from coffee houses towards a more modern stock exchange model.

In 1697, Parliament passed an Act to regulate stock market brokers at the Royal Exchange, imposing heavy penalties on unlicensed brokers and setting a limit on the number of brokers at 100.

The London Stock Exchange was founded in 1698, making it one of the oldest stock exchanges globally with a history spanning over 300 years.

In 1773, Jonathan and 150 other brokers formed a club and opened a more formal Stock Exchange in Sweeting's Alley, with a set entrance fee for traders to trade securities.

On Tuesday, August 27, 1776, a London Stock Exchange Broadsheet was published by Antipodean Books, Maps, and Prints, providing information on the Course of the Exchange. This publication likely contained details on stock prices and market trends.

In 1801, the first regulated exchange was established in London, marking the birth of the modern Stock Exchange.

In February 1812, the General Purpose Committee confirmed a set of recommendations that later became the foundation of the first codified rule book of the Exchange. The document addressed topics such as settlement and default, despite not being complex.

In 1830, the flow of financial information in the London Stock Exchange was transformed with the introduction of the electric telegraph for transmitting prices by ticker tape.

In 1836, both the Manchester and Liverpool stock exchanges were opened, reflecting the economic growth in these cities. Stock prices experienced significant fluctuations during this period, attracting entrepreneurs to the stockbroking profession.

In March 1854, the Exchange's new brick building, designed by architect Thomas Allason and inspired by the Great Exhibition, was completed. This expansion provided twice the floor space, alleviating the overcrowding issues.

In 1923, the Stock Exchange received its own coat of arms with the motto 'Dictum Meum Pactum' (My Word is My Bond), symbolizing the commitment to trust and integrity in trading.

The London Stock Exchange was closed for one day in 1945 due to damage from a V-2 rocket during wartime, but trading continued in the basement.

Queen Elizabeth II opened the new Stock Exchange Tower on 8 November 1972, marking a new City landmark with a 321 feet high building and a 23,000 sq ft trading floor.

In 1973, the regional exchanges in the United Kingdom were merged to form the Stock Exchange of Great Britain and Ireland, which was later renamed the London Stock Exchange (LSE).

The FTSE 250 Index marked its 35th anniversary in October 2017. This index includes the 101st to the 350th largest companies listed on the London Stock Exchange, reflecting the performance of mid-cap stocks.

The FTSE 100 Index, launched on 3 January 1984 by a partnership of the Financial Times and the Stock Exchange, became one of the most useful indices tracking the movements of the top 100 companies listed on the Exchange.

The Big Bang refers to the government's deregulation of the London stock market on October 27, 1986. This event led to a modernized electronic trading system and opened up the London Stock Exchange to capital markets worldwide.

On July 20, 1990, a bomb planted by the Provisional Irish Republican Army (IRA) exploded in the men's toilets behind the visitors' gallery at the London Stock Exchange. Despite a warning, the explosion caused damage to the building but no injuries.

In 1995, the Alternative Investment Market (AIM) was established by the London Stock Exchange. AIM is dedicated to supporting smaller, high-growth companies and has grown to become the leading growth market globally.

In 1999, the book 'The London Stock Exchange: A History' by R. C. Michie was published by Oxford University Press, providing a comprehensive account of the London Stock Exchange.

In 2000, the shareholders of the London Stock Exchange voted to transform it into a public limited company, London Stock Exchange plc, marking a significant change in its structure and governance.

In July 2001, the London Stock Exchange transitioned into a public company and was listed on its own market.

In 2003, EDX London, an international equity derivatives business, was established in partnership with OM Group, enhancing the London Stock Exchange's offerings in the derivatives market.

In December 2005, LSE rejected a £1.6 billion offer from Macquarie Bank and later turned down an unsolicited approach from NASDAQ valuing the company at £2.4 billion. NASDAQ eventually acquired a 15% stake in LSE.

Within a month or two of waiting as required by UK financial rules, NASDAQ increased its stake in the London Stock Exchange to 28.75% and launched a hostile offer at £12.43 per share, which was the highest price NASDAQ had paid for its existing shares.

NASDAQ revised its offer for the London Stock Exchange on 12 December 2006, indicating that it would need 50% of LSE's stock to complete the deal, instead of the initial 90% it sought. Despite the revision, the bid was still not deemed satisfactory by many stakeholders.

After receiving acceptances of only 0.41% of the LSE shares by the deadline on 10 February 2007, NASDAQ's offer to take over the London Stock Exchange was rejected by its shareholders.

On June 23, 2007, London Stock Exchange (LSE) announced a recommended offer to the shareholders of Borsa Italiana S.p.A, leading to the merger of the two companies. This merger created a diversified exchange group in Europe, known as the London Stock Exchange Group.

On 20 August 2007, NASDAQ announced that it was abandoning its plan to acquire the London Stock Exchange and would explore options to divest its 31% shareholding in the company following the failed takeover attempt.

On 16 September 2009, the London Stock Exchange Group agreed to purchase Millennium Information Technologies, Ltd., a Sri Lankan-based software company specializing in trading systems.

In November 2010, London Stock Exchange Group (LSEG) acquires a majority stake in Turquoise, the pan-European equities trading platform, which it owns in partnership with leading global investment banks.

On February 9, 2011, London Stock Exchange Group announced a merger with Toronto-based TMX Group, creating a combined entity with a market capitalization of £3.7 trillion. The merger was later terminated on June 29, 2011, due to lack of shareholder approval.

On June 29, 2011, London Stock Exchange Group announced the termination of the merger with TMX Group, citing lack of required shareholder approval from TMX Group. Despite obtaining support from its own shareholders, the merger failed to materialize.

In January 2014, the FTSE 100 Index, a key stock market index in the UK, celebrated its 30th anniversary. The index includes the top 100 companies listed on the London Stock Exchange based on market capitalization.

In May 2015, London Stock Exchange Group (LSEG) completed the acquisition of Frank Russell Company, a US-based financial services provider known for its Russell Indexes business.

In May 2015, FTSE and Russell Indexes combined to form FTSE Russell, creating a major player in the global financial market index sector.

In March 2016, London Stock Exchange announced a merger agreement with Deutsche Börse to create a new holding company, UK TopCo, with headquarters in London and Frankfurt.

In September 2016, CurveGlobal, an interest rate derivatives venture involving LSEG, leading dealer banks, and the Chicago Board Options Exchange, was introduced to the market.

On 25 February 2017, London Stock Exchange Group PLC decided not to sell its fixed-income trading platform in Italy to Deutsche Börse AG to address anti-trust concerns.

The planned merger between London Stock Exchange and Deutsche Börse was blocked by the EU Competition Regulator on 29 March 2017 due to concerns of creating a monopoly in the markets for clearing fixed income instruments.

In December 2018, LSEG raised its majority shareholding in LCH to 82.6 per cent.

On 11 September 2019, LSEG became the target of a £32 billion bid by Hong Kong Exchanges and Clearing, contingent on abandoning the plans to buy Refinitiv.

On 18 September 2020, LSEG entered exclusive talks to sell the Italian Bourse to Euronext, which was later announced and completed in 2021.

On 9 October 2020, LSE agreed to sell Borsa Italiana, including MTS, to Euronext for €4.3 billion. The acquisition was completed on 29 April 2021 for €4,444 million.

On March 3, 2022, the London Stock Exchange announced the suspension of trading in Global Depositary Receipt (GDR) securities for Russian firms following the 2022 Russian invasion of Ukraine.

On 12 Dec 2022, Microsoft purchased a nearly 4% stake in London Stock Exchange Group as part of a ten-year cloud deal.

As of June 21, 2023, the largest companies by market capitalization listed on the London Stock Exchange (LSE) include AstraZeneca PLC, Shell PLC, HSBC Holding PLC, Unilever PLC, and BP PLC.

The company was listed on the London Stock Exchange on April 26, 2024.