On June 16, 1911, the four companies of, Julius E. Pitrap (patented the computing scale), Alexander Dey (inventing the dial record), Herman Hollerith (patented the Electric Tabulating Machine), and Willard Bundy (invented a time clock to record a worker's arrival and departure time on paper tape), amalgamated in New York State by Charles Ranlett Flint forming a fifth company, the Computing-Tabulating-Recording Company (CTR) based in Endicott, New York.

In 1914, Thomas J. Watson, Sr., fired from the National Cash Register Company by John Henry Patterson, was offered a position at CTR. Watson joined CTR as General Manager.

In 1915, Watson was made President when court cases relating to his time at NCR were resolved. Having learned Patterson's pioneering business practices, Watson proceeded to put the stamp of NCR onto CTR's companies. His favorite slogan, "THINK", became a mantra for each company's employees.

During Watson's first four years, revenues reached $9 million, $133 million today, and the company's operations expanded to Europe, South America, Asia, and Australia.

Watson never liked the clumsy hyphenated name "Computing-Tabulating-Recording Company" and on February 14, 1924, chose to replace it with the more expansive title "International Business Machines".

By 1933 most of the subsidiaries had been merged into one company, IBM.

In 1937 IBM's tabulating equipment enabled organizations to process huge amounts of data. Its clients included the U.S. Government, during its first effort to maintain the employment records for 26 million people pursuant to the Social Security Act.

In 1937 IBM enabled Hitler's Third Reich to track the Jews and other persecuted groups, largely through the German subsidiary Dehomag.

In 1949 Thomas Watson, Sr., created IBM World Trade Corporation, a subsidiary of IBM focused on foreign operations.

In 1952, Thomas Watson, Sr. stepped down after almost 40 years at the company helm, and his son Thomas Watson, Jr. was named president.

In 1956 the company demonstrated the first practical example of artificial intelligence when Arthur L. Samuel of IBM's Poughkeepsie, New York, laboratory programmed an IBM 704 not merely to play checkers but "learn" from its own experience.

In 1957, IBM developed FORTRAN scientific programming language by the American computer scientist John Backus.

In 1961 IBM developed the SABRE reservation system for American Airlines and introduced the highly successful Selectric typewriter.

In 1963 IBM employees and computers helped NASA track the orbital flights of the Mercury astronauts.

On 7 April 1964, IBM announced the first computer system family, the IBM System/360. It spanned the complete range of commercial and scientific applications from large to small, allowing companies to upgrade to models with greater computing capability without having to rewrite their applications.

In 1964, IBM moved its corporate headquarters from New York City to Armonk, New York.

The latter half of the 1960s saw IBM continue its support of space exploration, participating in the 1965 Gemini flights, 1966 Saturn flights, and 1969 lunar mission.

In 1969, IBM engineer Forrest Parry invented the magnetic stripe card that would become ubiquitous for credit/debit/ATM cards, driver's licenses, rapid transit cards, and a multitude of other identity and access control applications.

IBM pioneered the manufacture of magnetic cards, and for most of the 1970s, the data processing systems and software for such applications ran exclusively on IBM computers.

In 1970, IBM System/370 was introduced. Together the 360 and 370 made the IBM mainframe the dominant mainframe computer and the dominant computing platform in the industry throughout this period and into the early 1980s.

In 1974 IBM engineer George J. Laurer developed the Universal Product Code.

Five IBMers have received the Nobel Prize: Leo Esaki, of the Thomas J. Watson Research Center in Yorktown Heights, N.Y., in 1973, for work in semiconductors; Gerd Binnig and Heinrich Rohrer, of the Zurich Research Center, in 1986, for the scanning tunneling microscope, and Georg Bednorz and Alex Müller, also of Zurich, in 1987, for research in superconductivity.

IBM and the World Bank first introduced financial swaps to the public in 1981 when they entered into a swap agreement.

In 1981, the IBM PC, originally designated IBM 5150, was introduced, and it soon became an industry standard.

In 1991 IBM spun out its printer manufacturing into a new business called Lexmark, a privately held American company that manufactures laser printers and imaging products. The company is headquartered in Lexington, Kentucky.

In 1993 IBM posted an US$8 billion loss – at the time the biggest in American corporate history. Lou Gerstner was hired as CEO from RJR Nabisco to turn the company around, on 1 April 1993.

In 2003, after acquiring PwC consulting, IBM initiated a project to redefine company values, hosting a three-day online discussion of key business issues with 50,000 employees. The result was three values: "Dedication to every client's success", "Innovation that matters—for our company and for the world", and "Trust and personal responsibility in all relationships".

On 1 May 2005, the company sold its personal computer business to the Chinese technology company Lenovo for US$1.25 billion.

IBM was recognized as one of the Top 20 Best Workplaces for Commuters by the United States Environmental Protection Agency (EPA) in 2005, which recognized Fortune 500 companies that provided employees with excellent commuter benefits to help reduce traffic and air pollution.

In 2009, it acquired software company SPSS Inc.

Later in 2009, IBM's Blue Gene supercomputing program was awarded the National Medal of Technology and Innovation by U.S. President Barack Obama.

In 2011, IBM gained worldwide attention for its artificial intelligence program Watson, which was exhibited on Jeopardy! where it won against game-show champions Ken Jennings and Brad Rutter.

In 2012, IBM celebrated its 100th anniversary.

In 2012 IBM announced it has agreed to buy Kenexa.

In 2013, IBM also acquired SoftLayer Technologies, a web hosting service, in a deal worth around $2 billion.

Also, in 2013, the company designed a video surveillance system for Davao City.

In 2014 IBM announced it would sell its x86 server division to Lenovo for $2.1 billion.

In 2014, the company revealed TrueNorth, a neuromorphic CMOS integrated circuit, and announced a $3 billion investment over the following five years to design a neural chip that mimics the human brain, with 10 billion neurons and 100 trillion synapses, but that uses just 1 kilowatt of power.

Also, in 2014, IBM began announcing several major partnerships with other companies, including Apple Inc., Twitter, Facebook, Tencent, Cisco, UnderArmour, Box, Microsoft, VMware, CSC, Macy's, Sesame Workshop, the parent company of Sesame Street, and Salesforce.com.

In May 2015, Groupon sued IBM accusing it of patent infringement, two months after IBM accused Groupon of patent infringement in a separate lawsuit.

In 2015 IBM announced three major acquisitions: Merge Healthcare for $1 billion, data storage vendor Cleversafe, and all digital assets from The Weather Company, including Weather.com and the Weather Channel mobile app.

In 2016, IBM acquired video conferencing service Ustream and formed a new cloud video unit.

In April 2016, it posted a 14-year low in quarterly sales.

In 2016, IBM bought Truven Health Analytics for $2.6 billion.

IBM's shares traded at over $125 per share, and its market capitalization was valued at over US$113.9 billion in September 2018.

In October 2018, IBM announced its intention to acquire Red Hat for $34 billion.

IBM ranked No. 34 on the 2018 Fortune 500 rankings of the largest United States corporations by total revenue.

On 9 July 2019, IBM succeeded to buy Red Hat for $34 billion.

In March 2020 it was announced that IBM will build the first quantum computer in Germany. The computer should allow researchers to harness the technology without falling foul of the EU's increasingly assertive stance on data sovereignty.

In 2020, the company holds the record for most patents generated by a business, marking 27 consecutive years for the achievement.