James attended Harvard College, where he was a John Harvard Scholar, and graduated magna cum laude in 1973. He earned an MBA from Harvard Business School in 1975, where he was a Baker Scholar.

In August 1973, James married Amabel George Boyce, the daughter of Mr and Mrs John Cowman George Boyce of Lutherville and Wequetonsing, Michigan. They have three children, daughters Meredith Evans and Rebecca Lee and son Hamilton Boyce.

In 1975, James joined investment bank Donaldson, Lufkin & Jenrette and became head of its global M&A group in 1982. He founded DLJ Merchant Banking, Inc in 1985. In 1995, James was appointed chairman of the firm’s banking group, a position he held when DLJ was acquired in 2000 by Credit Suisse First Boston, and was a member of its board of directors. At CSFB, James served on the executive board and as chairman of global investment banking and private equity. A 2007 Wall Street Journal article credited James with leading the acquisition process, on behalf of DLJ.

In 2002, James joined global alternative asset manager The Blackstone Group, where he was president and chief operating officer. He is on the firm’s executive and management committees, and its board of directors. He has been credited with reorganizing Blackstone’s management and creating its executive committee.

James was directly implicated in a 2007 corporate collusion conspiracy among fellow private equity giants Bain Capital and Carlyle Group. Alongside Blackstone, these firms rigged bids in 19 leveraged buyouts and eight other transactions. James wrote in an email to KKR co-founder George Roberts “Together we can be unstoppable but in opposition we can cost each other a lot of money.” James also sent a note to his Blackstone colleagues about the co-founder of another private equity group, KKR: “Henry Kravis just called to say congratulations and that they were standing down because he had told me before they would not jump a signed deal of ours.” Though the PE firms tried to dismiss the case, a federal judge denied their motion. Ultimately, the case was settled out of court in 2014. The firms paid the plaintiffs about $600 million.

James has donated to both Republican and Democratic politicians and institutions. He was a major Republican donor from 2000 – 2008, and even gave slightly more to Republicans than Democrats in the 2008 presidential election. He contributed about $130,890 to Republicans in the Bush era. Under President George W. Bush, James served as a member of the President’s Export Council’s Subcommittee on Technology and Competitiveness.

In 2008 James became a regular donor and fundraiser host for Barack Obama. In May 2012, James, a Democrat, hosted a fundraiser at his home in New York for President Barack Obama, raised more than $2 million for the President’s reelection campaign. Obama offered James the job of Commerce Secretary but he ultimately turned it down.

In 2011, it was confirmed that James had spent $24.9 million on an apartment at 834 Fifth Avenue, New York City, previously owned by Hal Prince, having lived at 1001 Park Avenue since the 1980s.

In 2015, James was appointed to the Port Authority Board of Commissioners despite his lack of experience with transportation issues, and in spite of Blackstone recently having purchased half of fellow commissioner Scott Rechler’s New York real estate portfolio.

In August 2017, James was appointed chairman of Costco after the death of co-founder and long-time chairman Jeffrey Brotman.

In November 2020 he was named Co-Chair of the Board of the Metropolitan Museum of Art with Candace Beinecke, effective January 12, 2021, the first time the museum had two chairs.