Confidential (1997), Deep Impact (1998), The Green Mile (1999), Space Cowboys (2000),[2] The Longest Yard (2005)[3] The Queen (2006), W. (2008), Secretariat (2010), The Artist (2011), Still Mine (2013), The Promise (2016), Marshall (2017), Jurassic World: Fallen Kingdom (2018), and Emperor (2020).

Cromwell is also well known for his roles in television including Angels in America (2003), Six Feet Under (2003–2005), American Horror Story: Asylum (2012–2013), for which he won the Primetime Emmy Award for Outstanding Supporting Actor in a Miniseries or a Movie, Boardwalk Empire (2012–2013), The Young Pope (2016), Counterpart (2018–2019), Succession (2018–2023), for which he earned three Primetime Emmy Award nominations for Outstanding Guest Actor, and Sugar (2024).

In 1975, he took his first lead role on television as Bill Lewis in the short-lived Hot l Baltimore, and appeared on M*A*S*H as Captain Leo Bardonaro in the episode "Last Laugh".

In 1980, Cromwell guest-starred in the two-part episode "Laura Ingalls Wilder" of the long-running television series Little House on the Prairie.

[citation needed] While Cromwell continued with regular television work throughout the 1980s, he made appearances in films with supporting roles in Tank and Revenge of the Nerds (both 1984).

The following year, he received his second Emmy Award nomination for playing Bishop Lionel Stewart on the NBC medical drama series ER.

From 2003 to 2005, Cromwell played George Sibley in the HBO drama series Six Feet Under, which earned him his third Emmy Award nomination in 2003.

The following year, Cromwell played Prince Philip, Duke of Edinburgh in The Queen (2006), that earned Helen Mirren an Academy Award for Best Actress.

He also guest-starred as Phillip Bauer, father of lead character Jack, in the sixth season of the Fox thriller drama series 24.

In 2015, Cromwell executive produced the documentary Imminent Threat which tackles the War on Terror's impact on civil liberties.

[25] Cromwell starred in Operation Buffalo, an Australian television comedy-drama series about the atomic bomb tests in outback Australia, which screened on ABC from 31 May 2020.

[30] In 2017, he was arrested during a PETA protest against SeaWorld's treatment of orca whales, at which he spoke about marine mammals' suffering and premature deaths.

[33][34] The incident, which garnered widespread press coverage, was resolved on March 25, 2013, when an attorney representing Cromwell entered no-contest pleas to the non-criminal offense and agreed to pay $100 forfeitures and court costs of $263.50.

[42] Cromwell and fellow Star Trek actor J. G. Hertzler were among the 19 people arrested in Watkins Glen, New York, on June 6, 2016, for a protest against underground gas storage in salt caverns near Seneca Lake.

[43] On June 6, 2017, he was escorted out of a Democratic Party fundraiser (which New York Governor Andrew Cuomo and House Minority leader Nancy Pelosi attended) after disrupting the event by protesting about the power station.

[44] Cromwell was again arrested, this time for trespassing after taking part in a protest along with People for the Ethical Treatment of Animals (PETA) at Seaworld on July 24.

Cromwell's experiences of the Civil Rights Movement while on a theatre tour through several Deep South states in 1964 had a profound effect on him.

[58] In an October 2008 interview, Cromwell criticized the Republican Party and the George W. Bush administration, saying that their foreign policy would "either destroy us or the entire planet".