Jack Dorsey grew up in St. Louis, Missouri, and by age 13, he had become interested in dispatch routing. Some of the open-source software he created in the area of dispatch logistics is still used today by many taxi cab companies. He went to high school at Bishop DuBourg High School and attended the Missouri University of Science and Technology before subsequently transferring to New York University, where he first conceived the idea for Twitter.

As Chief Executive Officer, Dorsey saw Twitter through two rounds of funding by the venture capitalists who backed the company. On 16 October 2008, Evan Williams took over the role of CEO and Dorsey became chairman of the board. On 28 March 2011, Dorsey returned to Twitter as Executive Chairman. As the service grew in popularity, Dorsey chose improving uptime as a top priority, even over creating revenue - which, as of 2008, Twitter was not designed to earn. Dorsey described the commercial use of Twitter and its API as two things that could lead to paid features. His three guiding principles, which are shared by the whole company and through its culture, are simplicity, constraint and craftsmanship.

Jack Dorsey developed a small business platform to accept debit and credit cards on a mobile device - initially called Square, now rebranded as Block - released in May 2010. The small, square-shaped device attaches to iPhone, iPad or Android devices via the headphone jack, and as a mini card reader allows a person to swipe their card, choose an amount to give to the recipient and then sign their name for confirmation. Square is also a system for sending paperless receipts via text message or email, and is available as a free app for iOS and Android OS. The company grew from 10 employees in December 2009 to over a hundred employees by June 2011.