[1] Steadman made her professional stage debut in 1968 and went on to establish her career in Mike Leigh's 1970s TV plays Nuts in May (1976) and Abigail's Party (1977).

[2] She received BAFTA TV Award nominations for the 1986 BBC serial The Singing Detective and in 2001 for the ITV drama series Fat Friends (2000–2005).

[4] Having left the East 15 Acting School in Loughton, Essex, Steadman worked in various regional repertory theatres, starting at Lincoln in 1968, where her first role was the schoolgirl Sandy in The Prime of Miss Jean Brodie.

She created the role of the monstrous Beverly in Mike Leigh's Abigail's Party, which she reprised with the original cast on television.

[citation needed] 2002 saw her play the role of Hillary in Debbie Isitt's The Woman Who Cooked Her Husband at the West End's Ambassadors Theatre to widely positive reviews.

[8][9] Steadman has appeared in many films, including P'tang, Yang, Kipperbang (1982), Champions (1983), A Private Function (1984), Number One (1984), Clockwise (1986), Stormy Monday (1988), The Adventures of Baron Munchausen (1988), Shirley Valentine (1989), Wilt (1989), Life Is Sweet (1990), Blame It on the Bellboy (1992), Topsy-Turvy (1999), The Life and Death of Peter Sellers (2004), Confetti (2006), Burn Burn Burn (2015), Dads Army (2016) and 23 Walks (2020), Steadman is credited with sharing the first lesbian kiss on British television with Myra Frances.

Other television work includes Fat Friends as Betty, Grumpy Old Women, Stressed Eric, Let Them Eat Cake, The Singing Detective, No Bananas, The Caucasian Chalk Circle, Adrian Mole: The Cappuccino Years as Pauline Mole, opposite James Bolam in the television film The Missing Postman, and Pride and Prejudice as Mrs. Bennet.

In 2007 she featured in the BBC Wales programme Coming Home about her Welsh family history, with roots in Trefarclawdd and Ruabon.

Also in 2018 she featured in ITV1 mini series Butterfly where she played Maxine Duffy’s Grandmother On radio, Steadman's talent for mimicry and character voices was given full rein in the 1970s, mainly at BBC Manchester, in comedy sketch shows including Week Ending, Castle's on the Air and The Worst Show on the Wireless.

In the early to mid 1980s Steadman also had a spell in Roy Hudd's long-running comedy sketch series The News Huddlines.