Mavis was born in Weatherfield but was brought up in Grange-over-Sands. By 1971, she was back in Weatherfield and working at the Mark Brittain Warehouse, but two years later she left the job to take the assistant position at The Kabin. Rita was Mavis's closest friend in the Street, although they were quite different; while Mavis was indecisive and dowdy, Rita was confident and glamorous. Mavis was easily misled and Rita often tried to protect her, usually from herself.
One of Mavis's greatest fears was that she would never marry. She was always surprised when men showed an interest in her, leading her to doubt any man was a good match for her. This was especially true with regards to Derek Wilton, who was just as indecisive; he and Mavis agreed to marry in 1984 but neither of them showed up at the church. Derek and Mavis had an on-off relationship for many years but finally got properly married in 1988, and two years later bought the new No.4 Coronation Street.
When Derek died in 1997, Mavis found it too hard to live at No.4 without him and moved to the Lake District to run a bed and breakfast. Aside from Derek, Mavis's suitors included Jerry Booth, Victor Pendlebury and Carlos, who asked Mavis to marry him in 1975 so that he could stay in the country. Another key relationship was with her pet budgie Harriet, which Mavis was always making a fuss over.
In 1983, her life changed, when not one, but two, men wanted to marry her. She wanted both of them, but had to choose between Victor Pendlebury or Derek Wilton. In the end she choose Derek, but jilted him at the altar as she wasn't convinced of the strength of her feelings for him. Her guilt at having done this turned to indignation when she learned that Derek had jilted her too, as he felt the same.
However, Mavis finally decided Derek was the man for her. When Mavis finally said "I do" to him in November 1988, she meant it. Her marriage to Derek was an unusual one - the other residents of Coronation Street looked upon them as something of a joke, but neither cared as they had each other. They would spend evenings reading aloud to each other from the newspapers and discussing the events of the day.
Their happiness was cut short in April 1997, when Derek died suddenly. Mavis was quick to hit out at his funeral at the people who had considered them a joke, saying that they had loved each other and that was all that mattered.
Mavis surprised Rita when she suggested that they should go into business together. They discussed the possibility of running a guest house in Cartmel, a town in the Lake District. Rita went along with this for a while, but both realised it was a bad idea - as Rita said "We'd end up throttling each other before t'week were out." Mavis went ahead with the idea, bought the guest house, and Mavis and Rita had an emotional farewell, ending a partnership of twenty-five years.
- In her early one-off appearances from 1971 to 1972, the character was credited as "Miss Riley".
- Thelma Barlow had quit the role of Mavis in 1997 after playing the character for twenty-five years. However, it was originally believed that she had quit the role due to the axing of her colleague Peter Baldwin, who played Mavis's husband Derek Wilton, who was axed by producer Brian Park. Despite this popular belief, Thelma confirmed on the programme This Morning in 2010 that she had quit the role before Mr Park came to the decision of axing Derek.
- Rita Sullivan visited Mavis in 1998 and 1999 at her home in Cartmel, and they holidayed on a cruise together in 2002. Emily Bishop stayed with Mavis in July 2004. In 2012 Rita attempted to visit Mavis, but was pulled over for speeding by a colleague of Kirsty Soames who was trying to get Tina McIntyre into trouble. Rita took a weekday break in February 2015, to visit Mavis who had recently lost nine pounds from a diet. In September 2017, Rita told Gemma that she wished she invested more in her relationship with Mavis since she left Weatherfield as they currently only exchanged birthday and Christmas cards.
First and last lines
"Excuse me." (First line, to Ena Sharples)
"I hope you will be too." (Final line, in response to Rita Sullivan's wish that she'll be happy in her new life)