His other notable roles include Working Girl (1988), Flatliners (1990), Beethoven (1992), Indecent Proposal (1993), A Time to Kill (1996), Bulworth, Dr. Dolittle (both 1998), Ready to Rumble (2000), Kinsey (2004), 2012 (2009), Love & Other Drugs (2010), X-Men: First Class (2011), Ginger & Rosa (2013), and Rules Don't Apply (2016).

"[10] Platt's family made frequent trips back to Washington, where they held Redskins season tickets.

[11] When he was nine years old, Platt and his family visited the Kennedy Center in Washington, where he watched a performance that helped inspire his acting career.

"[16] Platt travelled with Shakespeare and Company, based in Lenox, Massachusetts, touring schools to earn his Equity card, before moving to New York.

[16] He obtained an agent while working at Manhattan Punch Line Theatre, and met actor Bill Murray at his cousin's Christmas party.

[16] After Married to the Mob, he appeared in Working Girl (1988), Flatliners (1990), Beethoven (1992), The Three Musketeers (1993), A Time to Kill (1996), Executive Decision (1996), and Bulworth (1998).

[18] In 1999, Platt played the wealthy and eccentric crocodile enthusiast Hector in David E. Kelley's Lake Placid, alongside Bill Pullman and Bridget Fonda.

The strong cast, which also included Bebe Neuwirth and Hope Davis, could not compensate for substandard writing and the series was soon canceled.

[16][20] After Deadline's failure, Platt avoided work on television until he read a script for The West Wing and signed on for a guest role.

[16] He received an Emmy nomination for his portrayal of no-nonsense White House Counsel Oliver Babish,[16] brought in during season two to compile a defense for President Bartlet and others who covered up his non-disclosure of multiple sclerosis.

[21] His role in the television series Huff as Russell Tupper from 2004 to 2006 was well-received, especially by creator Bob Lowry, who said, "Oliver plays an alcoholic, drug-addicted, sexaholic, workaholic, womanizing misogynist who is adorable.

[16][22] In 2005, Platt acted in Harold Ramis's film The Ice Harvest as an unhappy businessman with a trophy wife and two stepchildren who becomes involved with a friend who has stolen $2 million from a Mafia boss.

[23] Platt won the New York Film Critics Online Award for best supporting actor for his role in Casanova.

[26] Platt signed onto the project after John Turturro was confirmed as Billy Martin, because "This thing lives or dies by that portrayal ...

[22] Platt starred as Nathan Detroit, alongside Lauren Graham as Miss Adelaide, in the Broadway revival of Guys and Dolls which began performances at the Nederlander Theatre on February 3, 2009, and officially opened on March 1, 2009.

[28] Platt starred as White House Chief of Staff Carl Anheuser in Roland Emmerich's 2012, a disaster film released November 13, 2009.

[29] In 2012, he starred in the romantic comedy The Oranges alongside Hugh Laurie and Leighton Meester[30] and appeared in the action film Chinese Zodiac.

[32] Platt married Mary Camilla Bonsal Campbell on September 12, 1992, at the First Congregational Church in Kittery, Maine.