Knox made her professional stage debut in 1962 at the Oldham Coliseum Theatre, had a small role as a dancer in the 1969 remake of Goodbye Mr. Chips and appeared opposite Ken Dodd in his 1972 comedy series Funny You Should Say That. For her part in perhaps her best remembered storyline in Coronation Street, involving the Alan Bradley character, she won the 1989 TV Times Award for Best Actress. In 2006, she won the British Soap Award for Best On-Screen Partnership with Malcolm Hebden, having previously received the Lifetime Achievement Award at the 2004 ceremony. She was made an MBE in the 2010 Queen's Birthday Honours.
Knox was born Barbara Brothwood in Oldham, Lancashire. Her mother worked in a mill while her father was a moulder at Platt's Foundry, and later a fireman.
Knox left school at 15 and worked as a telegraphist in the Post Office, learning shorthand and typing and had to pass Civil Service exams. She also worked in offices, shops and a factory. During this time she took part in amateur theatre until Carl Paulsen, who ran Oldham Rep, asked her to appear in The Boyfriend in 1962, which was her professional stage debut.
Knox later appeared in television programmes such as Never Mind the Quality, Feel the Width, George and the Dragon and A Family at War, as well as doing a stint in Emergency – Ward 10. She also had a small role as a dancer in the musical remake of Goodbye, Mr. Chips (1969) and did anything needed from announcer to stooge alongside several of the UK's top comedians for BBC radio's Comedy Half Hour. In 1972, she appeared opposite Ken Dodd in the sketch show Funny You Should Say That
Knox first played the role of Rita Littlewood in Coronation Street on 2 December 1964, when she appeared for only one episode as a friend of Dennis Tanner. She returned in January 1972 as Rita Bates, the common-law wife of Harry Bates, and in the decades since then the character has been married three times, to Len Fairclough, Ted Sullivan and Dennis Tanner. In 1973, she cut an LP for Philips Records entitled 'On the Street Where I Live.
Since 2010, she has given various interviews first on Paul O'Grady Live on ITV in November 2010, to coincide with Coronation Street's 50th anniversary, which also saw her appear in the ITV quiz show, Coronation Street: The Big 50. As well as two interviews on This Morning one in 2012 and another in 2013 as part of the 25 year anniversary and Knox's 80th birthday.
Knox also contributed to the one-off ITV documentary Coronation Street: A Moving Story, which saw the transition from recording at Granada Studios to the new MediaCityUK in 2014. On 31 December 2014, ITV celebrated Knox's contribution to Coronation Street with a special 60-minute documentary for 50 years as Rita called Rita and Me.
In 1989, Knox won the TV Times award for "Best Actress" and the Oracle Teletext "Best Actress" award for her part in the Alan Bradley storyline.
She won the "Best On-screen Partnership" award (jointly with Malcolm Hebden) at the British Soap Awards in May 2006 for her role as Rita Sullivan and in 2004, she won the "Life Time Achievement Award" for her services to Coronation Street.
Knox was appointed a Member of the Order of the British Empire (MBE) in the 2010 Birthday Honours, for services to drama.
Knox has been married twice. She married Denis Mullany in 1956 in Oldham, Lancashire. The couple had three children; Maxine, John and Amanda. They divorced in 1977. She was known professionally as Barbara Mullaney until 1977. She married John Knox in 1977. The couple divorced in 1994.
Knox, like her co-star Eileen Derbyshire, who plays Emily Bishop, shuns publicity and is a very private actress. She rarely gives interviews in public, although she has given a few interviews for Coronation Street documentaries and has appeared at some television awards shows.
On 28 March 2014 it was reported that she had been arrested on suspicion of driving while under the influence of alcohol in her home town of Knutsford, Cheshire. On 4 April Knox was formally charged, and she appeared at Macclesfield Magistrates' Court on 24 April. She pleaded not guilty and was scheduled to stand trial in July. This was later changed to a case hearing in October. On 23 January 2015 she changed her plea to guilty. She was banned from driving for a year, as well as being fined £3,000 and £1,750 in costs.