Keegan was born in Stockport, Greater Manchester, and attended St Patrick's RC High School in Salford, and later the Manchester School of Acting. Keegan worked at Selfridgesin the Trafford Centre shopping mall and as a check-in agent at Manchester Airport.
In late 2007, in only her second-ever audition, she was offered the chance to play the part of Tina McIntyre in Coronation Street, and accepted the role and she still plays this character to present day although on 20th April 2013, ITV announced her departure in May 2014. In 2009, she went on Stephen Mulhern's Anonymous a prank show on ITV. On 14 June 2009 Keegan made her radio debut co-hosting the BBC Radio 1 programme The Official Chart with Reggie Yates. Keegan was on the cover of FHM in January 2011, and placed #30 and #26 in their 100 Sexiest Women poll for 2010 and 2011 respectively.
Keegan dated Hollyoaks actor Anthony Quinlan from 2006 to 2008 and model Brad Howard from 2008–10. She began dating Mark Wright in January 2013. She also dated and was engaged to The Wanted's Max George after meeting him at one of their concerts but broke it off.