James attended Harvard College, where he was a John Harvard Scholar and from which he graduated magna cum laude in 1973. He received his MBA with high distinction from Harvard Business School in 1975, where he was a Baker Scholar.
In 1975, James joined investment bank Donaldson, Lufkin & Jenrette and became head of the firm's 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 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. Under President George W. Bush, James served as a member of the President's Export Council's Subcommittee on Technology and Competitiveness.
In 2013, James announced Blackstone LaunchPad's expansion into Montana. The Blackstone LaunchPad program is a $50 million initiative that aims to foster entrepreneurship across the country. Senator Jon Tester, who helped bring the program to Montana said, "It's about how you build an economy, how you better a state like Montana, how you keep this country on the cutting edge."
As of October 2015, he had a net worth of US$1.93 billion.
In 2017, The New York Times reported that The Metropolitan Museum of Art's Finance committee is led by James, who is also one of the board members at the Met. In August 2017, James was appointed chairman of Costco after the death of co-founder and long-time chairman Jeffrey Brotman.
James has supported the arts with endowments including the Amie and Tony James Gallery at CUNY Graduate Center in New York City, the Hamilton R. James Sculpture Acquisition Fund at the de Cordova Museum and Sculpture Park in Lincoln, Massachusetts, and the Waleska Evans James Gallery for the Karolik Collection of 19th Century American Landscapes at the Museum of Fine Arts in Boston.