After graduating, he worked in management consulting for two years before enrolling at Harvard Business School, along with classmates Jeff Immelt, Steve Burke, Stephen Mandel, and Seth Klarman. During the summer at Harvard, he worked at Goldman Sachs. He graduated in 1982, earning an MBA as a Baker Scholar.

In 1983, Dimon married Judith Kent, whom he met at Harvard Business School. They have three daughters: Julia, Laura, and Kara Leigh. Julia and Kara attended Duke University, while Laura is a Barnard College graduate and freelance journalist who formerly worked for New York Daily News.

Sandy Weill left American Express in 1985 and Dimon followed him. The two then took over Commercial Credit, a consumer finance company, from Control Data. At 30 years of age, Dimon served as the chief financial officer, helping to turn the company around. Through a series of mergers and acquisitions, in 1998 Dimon and Weill were able to form a large financial services conglomerate, Citigroup. Dimon left Citigroup in November 1998, after being asked to resign by Weill during a weekend executive retreat. It was rumored at the time that he and Weill argued in 1997 over Dimon’s not promoting Weill’s daughter, Jessica M. Bibliowicz, although that happened over a year before Dimon’s departure. At least one other account cites a request by Dimon to be treated as an equal as the real reason.

In March 2000, Dimon became CEO of Bank One, the nation’s fifth largest bank. When JPMorgan Chase purchased Bank One in July 2004, Dimon became president and chief operating officer of the combined company.

On December 31, 2005, he was named CEO of JPMorgan Chase and on December 31, 2006, he was named Chairman and President. In March 2008 he was a Class A board member of the Federal Reserve Bank of New York. Under Dimon’s leadership, with the acquisitions during his tenure, JPMorgan Chase has become the leading U.S. bank in domestic assets under management, market capitalization value, and publicly traded stock value. In 2009, Dimon was considered one of “The TopGun CEOs” by Brendan Wood International, an advisory agency.

As head of JPMorgan Chase, Dimon oversaw the transfer of $25 billion in funds from the U.S. Treasury Department to the bank on October 28, 2008, under the Troubled Asset Relief Program (TARP). This was the fifth largest amount transferred under Section A of TARP to help troubled assets related to residential mortgages. It has been widely reported that JPMorgan Chase was in much better financial shape than other banks and did not need TARP funds but accepted the funds because the government did not want to single out only the banks with capital issues. JPMorgan Chase advertised in February 2009 that it would be using its capital-base monetary strength to acquire new businesses.

By February 2009, the U.S. government had not moved forward in enforcing TARP’s intent of funding JPMorgan Chase with $25 billion. In the face of the government’s lack of action, Dimon was quoted during the week of February 1, 2009, as saying,

On September 26, 2011, Dimon was involved in a high-profile heated exchange with Mark Carney, the governor of the Bank of Canada, in which Dimon said provisions of the Basel III international financial regulations discriminate against U.S. banks and are “anti-American”. On May 10, 2012, JPMorgan Chase initiated an emergency conference call to report a loss of at least $2 billion in trades that Dimon said were “designed to hedge the bank’s overall credit risks”. The strategy was, in Dimon’s words, “flawed, complex, poorly reviewed, poorly executed, and poorly monitored”. The episode was investigated by the Federal Reserve, the SEC, and the FBI and the central actor was labelled with the epithet the London Whale.

Dimon commented on the Volcker Rule in January 2012, “Part of the Volcker Rule I agreed with, which is no prop trading. But market making is an essential function. And the public should recognize that we have the widest, the deepest, the most transparent capital markets in the world. And part of that is because we have enormous market making. If the rules were written as they originally came out; I suspect they’ll be changed, it would really make it hard to be a market maker in the United States.” He served as chairman of the executive committee of The Business Council for 2011 and 2012.

Dimon donates primarily to the Democratic Party. In May 2012, he described himself as “barely a Democrat” stating,

Dimon corrected that wrong information a month later, in May 2012, before the true damage was revealed, after US Securities and Exchange financial watchdog started reviewing the losses.

In the case of the 2012 JPMorgan Chase trading loss, according to a US Senate report published in March 2013 after 9 months of investigation, Dimon misled investors and regulators in April as losses rose dangerously to $6.2 billion on a “monstrous” derivatives bet made by the so-called “London Whale” Bruno Iksil. According to Carl Levin, chairman of this panel, JP Morgan had “a trading operation that piled on risk, ignored limits on risk taking, hid losses, dodged oversight and misinformed the public”. Dimon dismissed press accounts of possible losses in Iksil’s book as a “tempest in a teapot” on April 13, 2012 when he knew that Iksil had already lost $1 billion, which led Levin to say “None of those statements made on April 13 to the public, to investors, to analysts were true,” and “The bank also neglected to disclose on that day that the portfolio had massive positions that were hard to exit, that they were violating in massive numbers key risk limits.”

On January 24, 2014, it was announced that Dimon would receive $20 million for his work in 2013, a year of record profits and stock price under Dimon’s reign, despite significant losses that year due to scandals and payments of fines. The award was a 74% raise, which included over $18 million in restricted stock. This is despite the recent $13 billion settlement with the US government, the largest in history, for bad mortgages and practices during the financial crisis. Forbes reported that, in a statement following news of Dimon’s compensation, the bank said, “Under Mr. Dimon’s stewardship, the Company has fortified its control infrastructure and processes and strengthened each of its key businesses while continuing to focus on strengthening the Company’s leadership capabilities across all levels.”

Dimon was diagnosed with throat cancer in 2014. He received eight weeks of radiation and chemotherapy ending in September 2014. In March 2020, at the age of 63, Dimon underwent “emergency heart surgery.” The reason for the surgery was to repair an acute aortic dissection, a tear in the inner layer of the aorta, an artery that is the largest blood vessel in the body. According to JP Morgan, Dimon is recovering well from that surgery, with Gordon Smith and Daniel Pinto running the bank until his return.

In December 2016, Dimon joined a business forum assembled by then president-elect Donald Trump to provide strategic and policy advice on economic issues.