She is one of only two candidates to have declared themselves, the other being shadow business secretary Chuka Umunna (Streatham, south London).
Bookmakers have Mr Umunna as favourite with his closest challenger being shadow health secretary Andy Burnham (Leigh, Greater Manchester).
Former health minister Norman Lamb (North Norfolk) is to stand as Liberal Democrat leader with Tim Farron (Westmorland and Lonsdale, Cumbria) seen to be his biggest rival.
Mr Lamb tweeted:
Why I'm standing: see my Libdemvoice article - http://t.co/ykM6Snf58p— Norman Lamb (@normanlamb) May 12, 2015