Wiesel joined the J. Aron commodities division of Goldman Sachs in 1994, after the head of J. Aron strats convinced him to give up his initial preference of working in the video game industry. At the time, technology was in its earliest days in banking. At Goldman he worked for Lloyd Blankfein and Gary Cohn, who ended up leading the firm. One day Blankfein criticized him in the lobby of Goldman's headquarters as he arrived on rollerblades, saying: "I’m invested in that head, get a helmet!" He became a managing director in 2002, and a partner in 2004. Wiesel later served as the Chief Risk Officer of its securities division, and global head of its securities division desk strategists. In January 2017, when he was 44 years old, he succeeded R. Martin Chavez as Goldman's chief information officer, overseeing Engineering. Wiesel became the highest-ranked of 9,000 Goldman engineers, who accounted for 25% of the firm's total employees. In July 2017, Institutional Investor named him # 10 in the "2017 Tech 40." In December 2019 Wiesel left Goldman Sachs after a 25-year career at the firm. As he considers his next move, he said he was interested in the intersection of philanthropy and engineering and was ready to move on from banking. He was considering options that included traveling the world, computer games, and teaching, while intrigued by the health care company that Jeff Bezos, Warren Buffett, and Jamie Dimon were building, and committed to spending more time working on matters relating to his father such as deciding on the disposition of his papers.
Philanthropy
Wiesel organized fundraisers for Good Shepherd Services, a Brooklyn-based after-school program charity that provides support for at-risk youths and their families, at Goldman beginning in 2013. He also became well-known for organizing the popular all-night Midnight Madness problem-solving scavenger hunt throughout New York City, popular among Wall Street professionals. It has raised millions of dollars for charitable non-profits.
Political activity
At a November 30, 2016, event at the United States Holocaust Memorial Museum, Wiesel spoke of the need to protect the LGBT community and Israel, which he said was "treated as the world villain simply for making sure that Jews will never again be without a home," and criticized president-elect Donald Trump's policies. At another event held at the Museum of Jewish Heritage on January 29, 2017, he suggested that protesting against Executive Order 13769 was part of his father's legacy. In April 2017, in a speech to the March of the Living program at Auschwitz for Holocaust Remembrance Day, he said that the United States and European countries had not learned the lessons of the Holocaust, because many in those countries had turned away Syrian refugees fleeing chemical warfare. Wiesel added: "Will you stand by when African-Americans have reason to be terrified of a routine traffic stop, when Christians are slaughtered in Egypt because they are labelled infidels, when girls in Chad, Somalia, Afghanistan, and Pakistan are threatened, raped, or shot for pursuing an education, when homosexuality in Iran is a crime that carries the death penalty?"