In December 1965, the Korea International Steel Association was established.

On June 30, 1967, the Korean government chose Pohang as the location for an integrated steelworks.

In 1968, the South Korean government established Pohang Iron and Steel Company (POSCO) to achieve self-sufficiency in steel production and boost economic development. The construction of the Pohang plant began on this date.

On August 4, 1969, the Korean Government established a capacity target of 1.03 million tons for the Pohang Steel Mill.

On April 1, 1970, the construction of Phase 1 of the Pohang Steel Mill began.

On July 3, 1973, the Pohang steel plant of POSCO was dedicated with an initial annual capacity of 1.03 million metric tons. This marked a significant milestone in South Korea's steel industry development.

In May 1971, Pohang Industrial Furnace Co., Ltd. was established.

In 1972, the Pohang Steel Mill Phase 1 was successfully completed.

On March 2, 1973, the company surpassed the U$100 million mark in steel exports and the ₩100 billion mark in revenues.

On July 3, 1973, the company tapped the first batch of molten iron from Pohang Steelworks Blast Furnace No.1 at 7:30am.

On October 1, 1974, the Steel Education Foundation was established.

In 1975, POSCO laid the foundation for the first major expansion of overall production by developing high tensile strength steel. This advancement allowed the company to diversify its production capabilities.

On April 30, 1976, POSCO launched its Research and Development Center.

On May 31, 1976, POSCO made its first shipment of cold-rolled products.

On November 16, 1976, the construction of Pohang Steel Mill Phase 2 was successfully completed.

On January 1, 1977, the construction of Pohang Steel Mill Phase 3 was successfully completed.

On October 30, 1978, the Business Enhancement Committee was established.

On December 8, 1978, POSCO was selected as the builder and operator of the second steel mill.

On June 30, 1980, POSCO entered into a partnership agreement for the joint development of Green Hills Mine in Canada.

On January 21, 1981, the Nosa Labor-Management Council was established.

On February 18, 1981, Phase 4 of the Pohang Steel Mill was successfully finished.

By February 28, 1981, POSCO moved from being a state-invested enterprise to a state-financed one.

On November 4, 1981, Gwangyangman Bay was designated as the location for POSCO's second steelworks.

Gwangyang Steelworks, constructed in four phases between September 1982 and October 1992, is Korea's second integrated steelworks. It focuses on manufacturing automotive steel, high-strength structure steel, and other strategic products.

In December 1983, a fully automated factory for irregular-shaped refractories was constructed.

In March 1985, the construction of Gwangyang Steelworks Phase 1 began.

In December 1986, POSTECH was opened.

The construction of POSCO headquarters at 1 Goedong-dong, Nam-gu, Pohang, was completed on April 1, 1987. It serves as the central hub for overseeing major tasks such as management, planning, and finances of the steelworks at Pohang and Gwangyang.

An article by Joseph Manguno published in the Wall Street Journal on April 29, 1988, discussing the competition between a Korean steel firm and Japanese counterparts.

In 1989, POSCO opened itself to foreign ownership and began selling overseas convertible bonds to fund its expansion projects. This move marked a significant step towards internationalization for the company.

In 1991, POSCO significantly increased its steel exports to China, shipping over one million tons, marking a substantial growth from the previous year. This expansion was part of POSCO's strategy to tap into the nascent Chinese market.

In October 1992, the integrated construction was completed in time to celebrate a Quarter-century of Pohang Iron and Steel Co., Ltd. with an annual crude-steel capacity of 20.8 million tons.

In April 1993, a technology research center was established.

In July 1994, POSCO established two subsidiary companies, POSTEEL and POSTRADE. POSTEEL focused on domestic sales and services, while POSTRADE handled international trading of POSCO products.

In December 1994, the company underwent a name change to Pohang Iron and Steel Furnace Equipment Co., Ltd. as a result of the merger between Samhwa Hwasung and Keoyang Furnace.

In December 1995, POSCO opened the POSCO Center in Daechi-dong, Seoul, signaling the start of another proud chapter in the company's history.

In 1996, POSCO entered the Vietnamese market by launching a new plant, further diversifying its operations.

On November 25, 1997, POSCO concluded its first long-term iron ore offtake agreement with Hamersley.

The in-house newsletter Soetmul, meaning molten iron, was established on December 15, 1997.

In 1998, POSCO introduced a management commission and outside directorships to enhance its specialty and efficiency, laying the foundation for an advanced management system.

An article by Mi-Hui Kim in the Asian Wall Street Journal on February 2, 1999, revealing that POSCO made significant financial losses due to bad investments.

In October 2000, the privatization of POSCO was completed.

In April 2001, the company underwent another name change to POSREC Co., Ltd.

In March 2002, the company name was changed to POSCO Co., Ltd.

In July 2003, the company was listed on KOSDAQ, marking a significant milestone in its financial history.

In 2004, the company officially announced its Code of Ethics, outlining the principles and guidelines for ethical behavior within the organization.

In June 2005, POSCO signed a memorandum of understanding with the State of Orissa in India to invest $12 billion in constructing a steel plant with significant production capacity, promising to be a major foreign direct investment in India.

On June 30, 2006, POSCO finished building its sixth continuous galvanizing line at the Gwangyang mill in South Jeolla Province, solidifying its position as the second-largest producer of sheet steel globally.

In 2007, Warren Buffett's Berkshire Hathaway purchased a 4% stake in POSCO, showing confidence in the company's prospects. However, Berkshire later divested its shares in 2014.

In February 2008, the company achieved the Safety and Health Management System (KOSHA 18001) certification, demonstrating its dedication to ensuring a safe and healthy work environment for its employees.

The lime burning facility at Pohang Steelworks began operations in November 2008, contributing to the production processes and infrastructure of the steelworks.

In 2009, POSCO acquired Asian Stainless Corp in Vietnam.

In 2010, POSCO Chemtech underwent a name change to reflect its evolving business operations and strategies.

Ministry of Environment and Forests set up the N.C. Saxena committee in July 2010 to review the clearance for the POSCO project, which indicated violations of the Forest Rights Act.

In August 2010, POSCO Chemtech commenced the operation of a coke oven gas (COG) facility at Gwangyang Steelworks, enhancing its production capabilities.

In September 2010, POSCO Chemtech successfully acquired an anode materials business, expanding its product portfolio and market presence.

In November 2010, POSCO Chemtech initiated its COG by-product business, introducing new revenue streams and sustainable practices.

In December 2010, POSCO Chemtech was honored as one of the top 100 companies that significantly contributed to job creation, highlighting its positive impact on the economy.

Despite the N.C. Saxena committee's findings of Forest Rights Act violations, the Ministry of Environment and Forests issued final clearance to POSCO on January 31, 2011.

In January 2012, the company earned certification for Quality Management System (ISO 9001) and Environmental Management System (ISO 14001), showcasing its commitment to quality and environmental standards.

In May 2012, POSCO was chosen as the most respected company in South Korea. This recognition highlights the company's reputation and standing within the Korean business community.

In October 2012, a burned lime subsidiary was founded in Indonesia, expanding the company's operations internationally.

POSCO celebrated its 45th anniversary in 2013, marking 45 years of operation and contribution to Korea's history.

On January 15, 2014, the Central Government of India expressed confidence that with the renewal of environment clearance, the POSCO project in Odisha would progress.

The $12 billion Odisha project, initiated in 2005 as India's largest foreign direct investment, was cancelled in 2015 due to prolonged delays in land acquisition and opposition from local tribal groups. A new mining law enacted in March 2015 would have also required POSCO to obtain a mining license through auction.

In November 2016, discussions took place between POSCO executives and Arrium regarding the potential sale of the Whyalla Works, aiming to find a suitable buyer committed to long-term operations.

POSCO officially withdrew from the steel plant project in Odisha, India on March 18, 2017, after facing delays and regulatory approval issues. The project was initially agreed upon a decade ago with a planned investment of $12 billion USD.

In December 2018, POSCO marked a significant milestone by achieving 1.3 trillion won in sales, the largest in the company's history.

Following the merger with POSCO ESM, the energy material business was integrated into the company.

The marketable securities were transferred and listed on KOSPI exchange.

The cathode material plant in Gwangyang successfully completed phase 1 of its construction.

In August 2019, POSCO and Australia's Pilbara Minerals Ltd signed a binding terms sheet to establish a joint venture in South Korea for the development and operation of a lithium hydroxide and carbonate chemical conversion facility.

The second anode material plant completed phase 1 of its construction.

POSCO reported Total CO2e emissions (Direct + Indirect) for 31 December 2020 at 75,650 Kt (-4,614 /-5.7% y-o-y). This reflects the company's environmental impact and efforts to reduce carbon footprint.

In January 2021, P&O Chemical, a subsidiary, was founded to expand the company's operations.

In April 2021, the company raised its paid-in capital by a significant amount of 1,273.5 billion KRW.

In November 2021, the company celebrated its 50th anniversary since its establishment.

On January 13, 2022, the Adani Group announced a Memorandum of Understanding with POSCO to explore the establishment of an Integrated Steel Mill in Mundra, Gujarat, with an estimated investment of $5 billion USD.

In January 2023, the final phases 3 and 4 of the Gwangyang cathode production plant were completed.

In March 2023, a significant milestone was achieved as a 40 trillion KRW high-nickel cathode supply contract was secured with Samsung SDI.