Mir was born to first-generation Pakistani immigrants and brought up in the suburb of Bearsden, near Glasgow, from the age of ten. She graduated from the University of Bristol with an honours law degree in 1993.
In 1995 Mir had a brief stint as a reporter for the Daily Record and Sunday Mail, then became a radio researcher. In 2005 and 2006 she was a columnist for the Sunday Herald.
Mir began her career in broadcasting in 1992 appearing on a BBC TV programme called The Insiders with Gordon Kennedy. After graduation she joined Scottish Television aged 21 as a trainee and read the early morning news bulletins, and presented the main news show.
She presented a couple of editions of the documentary strand for BBC Two called East in 1996 and some items on Desi DNA. In 1998 she became a reporter for Central TV in Nottingham.
Mir has also presented Just Write on Channel 4 and Around Scotland on BBC Two. In 2010 she became a newspaper reviewer on GMTV with Lorraine and Lorraine.
In 1999 Mir moved to London as a producer for BBC Radio London and started doing freelance news-reading shifts for the national radio station BBC Radio 5 Live. She joined the station full-time in July 2001.
In April 2006 she covered the weekday morning phone in programme on BBC Asian Network for a fortnight when Sonia Deol left the programme, and before Anita Rani became presenter. She has presented items on the BBC Asian Network Report.
Mir presented the Midday News on 5 Live, Monday to Friday, until 9 January 2009. She joined BBC Scotland in April 2009 as a presenter of the Friday edition of Good Morning Scotland. Also in 2009 she presented a series of programmes for BBC Radio 4 on Scotland's Year of Homecoming, as well as Colour Me White for Radio 4, and Gay Life After Saddam for Radio 5 Live. In 2010 she replaced Anita Anand as a presenter of Radio 5 Live's Drive programme. In March 2012, for one week, she sat in for Jeremy Vine on his BBC Radio 2 programme.
On 27 September 2012 Mir announced on Twitter that she planned to leave BBC 5 Live, after 11 years with the station. Mir presented her last 5 Live Drive on 9 November 2012. On 29 October 2012 Mir presented BBC Radio 4 Woman's Hour. She has since presented the LBC 97.3 afternoon show as a substitute for Julia Hartley-Brewer.
She is a co-presenter of BBC Radio 4 Saturday Live (radio series).
Mir is married to Piara Powar, the executive director of Football Against Racism in Europe. Mir is an avid fan of Celtic.