Eisman grew up in New York City, where he attended Yeshiva schools. He attended the University of Pennsylvania, graduating magna cum laude in 1984. He then graduated from Harvard Law School with honors. His parents also worked in finance. They were brokers for Oppenheimer. Eisman was unhappy with his work in law. His parents arranged a position for him at Oppenheimer working as an equity analyst. Oppenheimer's anti-nepotism rules required his parents to pay the first year of his salary.
Eisman rose to fame betting against collateralized debt obligations at Greenwich, Connecticut-based FrontPoint Partners LLC, a unit of Morgan Stanley. By 2010, he managed more than $1 billion for FrontPoint, and gained prominence after being profiled by Michael Lewis in his book The Big Short: Inside the Doomsday Machine. In the movie adaptation of Lewis' book, The Big Short, Eisman's name was changed to Mark Baum, and was portrayed by actor Steve Carell. He left FrontPoint Partners in 2011 amid investor withdrawals following an investigation of illegal insider trading by portfolio manager Chip Skowron.
In 2012, Eisman founded Emrys Partners with $23 million in seed capital. The fund performed poorly in 2012, returning 3.6% and underperforming the market. It did better in 2013, returning 10.8% but still underperforming the market. In July 2014, he announced that he was shutting down the fund, explaining his decision by stating that "making investment decisions by looking solely at the fundamentals of individual companies is no longer a viable investment philosophy." The fund controlled an estimated $185 million in assets at the time of its dissolution. Emrys Partners stopped operating in mid-2014.
In September 2014, Eisman joined Neuberger Berman as a managing director and a portfolio manager for the Eisman Group within Neuberger Berman’s Private Asset Management division. The group, run by partners including Steve's parents, Elliott and Lillian Eisman, manages portfolios of stocks for wealthy clients.
He has been married to Valerie Feigen since 1989. Valerie was also portrayed in The Big Short under the name Cynthia, by Marisa Tomei. Feigen, who worked for J.P. Morgan, said of her husband, "Even on Wall Street people think he's rude and obnoxious and aggressive." While Eisman seems aware of his tendency to be rude he does not seem to be concerned by it. He once said to an interviewer on this topic, "I forget myself sometimes." Eisman's first-born son, Max, died after his night nurse rolled on top of him in her sleep. Eisman and his intimates describe the death of his son as a hugely influential event that affected him in many ways.