Abercrombie was born on 11 September 1934 in Grays, Essex, England. He began his theatrical career during the Blitz in World War II. After his footwork years during which he earned Bronze, Silver and Gold medals in stage dancing, he performed in London, Scotland, Ireland, and the Netherlands. He moved to the United States at age 17.

He made his American stage debut in 1955 in a production of Stalag 17 with Jason Robards and Jules Munshin. Many plays in summer stock, regional, and off-Broadway followed in a variety of theatrical offerings, from revues to Shakespeare (in a particularly low period, he worked as a magician's assistant for $10 a performance).

In 1957, he was drafted into the United States Army and stationed in West Germany as part of Special Services, where he directed the continental premiere of Separate Tables.

Abercrombie was known to cult film audiences as Wiseman in the comedy horror film Army of Darkness (1993). He guest-starred on many television series such as Seinfeld, The Nanny, Wizards of Waverly Place, Airwolf, Babylon 5 and NewsRadio.

Abercrombie portrayed Chancellor Palpatine / Darth Sidious in the 2008 film, the television adaptation, and two spin-off video games (Star Wars: The Clone Wars: Republic Heroes and Star Wars: The Clone Wars: Lightsaber Duels). Supervising Director Dave Filoni said that Ian was very excited that Darth Sidious finally was going to be seen in person and not as a hologram anymore; during Celebration VI, Filoni also mentioned that before his death, Ian did record for most of Season Five as both characters, but did not finish, so actor Tim Curry was brought in to voice Palpatine. However, Abercrombie also voiced the character in the Clovis story arc of the Lost Missions (Season Six) since it was originally a part of the Season Four, and later the Season Five, line-up. Thus, it was finished before his death. This was his final released work both on the series and in his life, shown in 2014. He was honored with a message of "In memory of Ian Abercrombie" at the beginning of Season 5, Episode 16 "The Lawless".

On radio, he was heard in several productions of the Hollywood Theater of the Ear. Abercrombie voiced Ambrose in Oscar-nominated Rango (2011). He also portrayed Ganthet on Green Lantern: The Animated Series, completing his work on the latest episode of Cartoon Network show just before his death.

Abercrombie died in Los Angeles, California on 26 January 2012, twenty days after the Wizards of Waverly Place finale, from kidney failure. He was 77.

In the United States, he went to California for a backers' audition, which went nowhere, but he began a long film and television career. He received awards for his work in Sweet Prince with Keir Dullea; Teeth 'N'smiles; A Doll's House with Linda Purl; and The Arcata Promise, opposite Anthony Hopkins. He received acclaim for the one-man show Jean Cocteau—A Mirror Image.