After completing his studies at the Academy, he joined Joan Littlewood’s Theatre Workshop. He began getting roles in West End theatre productions, starting with The Quare Fellow in 1956, a transfer from the Theatre Workshop. He spent nearly a decade in obscurity, learning his profession on stages throughout the UK.

In 1957, Harris married Elizabeth Rees-Williams, daughter of David Rees-Williams, 1st Baron Ogmore. They had three children: actor Jared Harris, actor Jamie Harris, and director Damian Harris. Harris and Rees-Williams divorced in 1969, after which Elizabeth married Rex Harrison. Harris’s second marriage was to the American actress Ann Turkel. In 1982, they divorced.

Harris made his film debut in 1959 in the film Alive and Kicking, and played the lead role in The Ginger Man in the West End in 1959. In his second film he had a small role as an IRA Volunteer in Shake Hands with the Devil (1959), supporting James Cagney. The film was shot in Ireland and directed by Michael Anderson who offered Harris a role in his next movie, The Wreck of the Mary Deare (1959), shot in Hollywood.

Harris’s first starring role was in the film This Sporting Life (1963), as a bitter young coal miner, Frank Machin, who becomes an acclaimed rugby league football player. It was based on the novel by David Storey and directed by Lindsay Anderson. For his role, Harris won Best Actor in 1963 at the Cannes Film Festival and an Academy Award nomination.

Harris paid £75,000 for William Burges’ Tower House in Holland Park in 1968, after discovering that the American entertainer Liberace had arranged to buy the house but had not yet put down a deposit. Harris employed the original decorators, Campbell Smith & Company Ltd., to carry out extensive restoration work on the interior.

Harris recorded several albums of music, one of which, A Tramp Shining, included the seven-minute hit song “MacArthur Park” (Harris insisted on singing the lyric as “MacArthur’s Park”). This song was written by Jimmy Webb, and it reached number 2 on the American Billboard Hot 100 chart. It also topped several music sales charts in Europe during the summer of 1968. “MacArthur Park” sold over one million copies and was awarded a gold disc. A second album, also consisting entirely of music composed by Webb, The Yard Went on Forever, was released in 1969. In the 1973 TV special “Burt Bacharach in Shangri-La”, after singing Webb’s “Didn’t We”, Harris tells Bacharach that since he was not a trained singer he approached songs as an actor concerned with words and emotions, acting the song with the sort of honesty the song is trying to convey. Then he proceeds to sing “If I Could Go Back”, from the Lost Horizon soundtrack.

He played the title role in the film Cromwell in 1970 opposite Alec Guinness as King Charles I of England. That year British exhibitors voted him the 9th-most popular star at the UK box office.

In 1971 Harris starred in a BBC TV film adaptation The Snow Goose, from a screenplay by Paul Gallico. It won a Golden Globe for Best Movie made for TV and was nominated for both a BAFTA and an Emmy. and was shown in the U.S. as part of the Hallmark Hall of Fame.

In 1973, Harris published a book of poetry, I, In the Membership of My Days, which was later reissued in part in an audio LP format, augmented by self-penned songs such as “I Don’t Know.”

At the height of his stardom in the 1960s and early 1970s Harris was almost as well known for his hellraiser lifestyle and heavy drinking as he was for his acting career. He was a longtime alcoholic until he became a teetotaler in 1981. Nevertheless, he did resume drinking Guinness a decade later. He gave up drugs after almost dying from a cocaine overdose in 1978.

Harris was a vocal supporter of the Provisional Irish Republican Army (PIRA) from 1973 until 1984. In January 1984 remarks he made on the previous month’s Harrods bombing caused great controversy, after which he discontinued his support for the PIRA.

Harris was a member of the Roman Catholic Knights of Malta, and was also dubbed a knight by the Queen of Denmark in 1985.

A lifelong supporter of Jesuit education principles, Harris established a friendship with University of Scranton President Rev. J. A. Panuska and raised funds for a scholarship for Irish students established in honour of his brother and manager, Dermot, who had died the previous year of a heart attack. He chaired acting workshops and cast the university’s production of Julius Caesar in November 1987.

In June 1989, director Jim Sheridan cast Harris in the lead role in The Field, written by the esteemed Irish playwright John B. Keane. The lead role of “Bull” McCabe was to be played by former Abbey Theatre actor Ray McAnally. When McAnally died suddenly on 15 June 1989, Harris was offered the McCabe role. The Field was released in 1990 and earned Harris his second Academy Award nomination for Best Actor. He lost to Jeremy Irons for Reversal of Fortune.

Over several years in the late 1980s, Harris worked with Irish author Michael Feeney Callan on his biography, which was published by Sidgwick & Jackson in 1990.

In 1992, Harris had a supporting role in the film Patriot Games. He had good roles in Unforgiven (1992), Wrestling Ernest Hemingway (1993) and Silent Tongue (1994). He played the title role in Abraham (1994) and had the lead in Cry, the Beloved Country (1995).

Harris appeared in two films which won the Academy Award for Best Picture. First, as the gunfighter “English Bob” in the Western Unforgiven (1992); second, as the Roman Emperor Marcus Aurelius in Ridley Scott’s Gladiator (2000). He also played a lead role alongside James Earl Jones in the Darrell Roodt film adaptation of Cry, the Beloved Country (1995). In 1999, Harris starred in the film To Walk with Lions. After Gladiator, Harris played the supporting role of Albus Dumbledore in the first two of the Harry Potter films, and as Abbé Faria in Kevin Reynolds’ film adaptation of The Count of Monte Cristo (2002). The film Kaena: The Prophecy (2003) was dedicated to him posthumously as he had voiced the character Opaz before his death.

Harris also made part of the Bible TV movie project filmed as a cinema production for the TV, a project produced by Lux Vide Italy with the collaboration of Radio Televisione Italiana RAI and Channel 5 of France, and premiered in the United States in the channel TNT in the 1990s. He portrayed the main and title character in the production Abraham (1993) as well as Saint John of Patmos in the 2000 TV film production Apocalypse.

Concerning his role as Dumbledore, Harris had stated that he did not intend to take the part at first, since he knew that his health was in decline, but he relented and accepted it because his 11-year-old granddaughter threatened to never speak to him again if he did not take it. In an interview with the Toronto Star in 2001, Harris expressed his concern that his association with the Harry Potter films would outshine the rest of his career. He explained, “Because, you see, I don’t just want to be remembered for being in those bloody films, and I’m afraid that’s what’s going to happen to me.”

Harris was diagnosed with Hodgkin’s disease in August 2002, reportedly after being hospitalised with pneumonia. He died at University College Hospital in Bloomsbury, London, on 25 October 2002, aged 72. He is survived by his three sons, Damian, Jared and Jamie. He spent his final three days in a coma. Harris’s body was cremated, and his ashes were scattered in the Bahamas, where he owned a home. His last words were “It was the food!”, uttered as he was being wheeled out of the Savoy Hotel.

On 30 September 2006, Manuel Di Lucia, of Kilkee, County Clare, a longtime friend, organised the placement in Kilkee of a bronze life-size statue of Richard Harris. It shows Harris at the age of eighteen playing the sport of squash. The sculptor was Seamus Connolly and the work was unveiled by Russell Crowe. Harris was an accomplished squash racquets player, winning the Tivoli Cup in Kilkee four years in a row from 1948 to 1951, a record unsurpassed to this day.

At the 2009 BAFTAs, Mickey Rourke dedicated his Best Actor award to Harris, calling him a “good friend and great actor”.

In 2013, Rob Gill and Zeb Moore founded the annual Richard Harris International Film Festival. The Richard Harris Film Festival is one of Ireland’s fastest-growing film festivals. Growing from just ten films in 2013 to screening over 115 films in 2017. Each year one of Harris’s sons attends the annual festival (October Bank Holiday Weekend) in Limerick.

On 25 June 2019, The New York Times Magazine listed Richard Harris among hundreds of artists whose master tapes were destroyed in the 2008 Universal fire.