[1][2] She is a Welsh-speaker: in the first volume of her autobiography Private Faces (1999) she notes that she spoke only Welsh for much of her childhood, learning English by listening to the radio.

[7][8][9] She won the Bancroft Gold Medal for Hedda Gabler and was offered work in Hollywood when she left RADA.

[11] Phillips began acting professionally at the age of 11 with the Home Service of BBC Radio in Wales.

At the same age she won her first speech-and-drama award for her performance at the National Eisteddfod held at Llandybïe in 1944, where she and a school friend played the parts of two elderly men in a dramatic duologue.

She performed as Princess Siwan in Saunders Lewis's The King's Daughter at the Hampstead Theatre Club in 1959 and as Katherine in Taming of the Shrew for the Oxford Playhouse in 1960.

[13][14] From October 1958 to April 1959, she was compere of the Land of Song (Gwlad y Gân) monthly programme at TWW (Television Wales and the West) Channel 10 with baritone Ivor Emmanuel.

An observer described her performance: "Sian Phillips' portrayal of Joan defies the law of averages, since, after seeing Siobhan McKenna in the 1955 Arts Theatre production, I reckoned it impossible to equal within half a century.

[24] Her Royal Shakespeare Company performances are: Her long career has included many films and television programmes, but she is perhaps best known for starring as Livia in the popular BBC adaptation of Robert Graves's novel I, Claudius (BBC2, 1976), for which she won the 1977 BAFTA Television Award for Best Actress, and for many appearances on the original run of Call My Bluff.

She also appeared opposite her then-husband Peter O'Toole and Richard Burton in Becket (1964); as Ursula Mossbank in the musical film Goodbye, Mr. Chips (1969), again starring O'Toole; once more opposite O'Toole in Murphy's War (1971); as Emmeline Pankhurst in the TV mini-series Shoulder to Shoulder (1974); as Clementine Churchill in Southern Television's Winston Churchill: The Wilderness Years (1981) starring Robert Hardy; as Lady Ann, the unfaithful wife of Alec Guinness's character George Smiley, in the BBC1 espionage dramas Tinker, Tailor, Soldier, Spy (1979) and Smiley's People (1982), adapted from John le Carré's eponymous novels; in Nijinsky (1980); and as the queen Cassiopeia in Clash of the Titans (1981).

Another popular role was that of the Reverend Mother Gaius Helen Mohiam in David Lynch's Dune (1984) and Charal from Ewoks: The Battle for Endor (1985).

She also appeared in seasons 2 and 4 (1998 and 2000) of the Canadian TV series La Femme Nikita as Adrian, the renegade founder of the powerful Section One anti-terrorist organisation.

[31] She provided spoken-word backing to a track on Rufus Wainwright's 2007 album Release the Stars and appeared live with him at the Old Vic Theatre in London on 31 May/1 June 2007.

The documentary includes Philips recounting, with candour, the difficulties in the later part of her marriage to O'Toole, which culminated in the ultimatum that she should leave the family home, without their two children, within the space of four hours.

The couple divorced in 1979, and Phillips wrote about this tempestuous period of her life in Public Places, the second volume of her autobiography.

[52] She is a patron of the Bird College of Dance, Music & Theatre Performance, based in Sidcup, Greater London.