The East Renfrewshire MP joins Lothian MSPs Neil Findlay and Sarah Boyack in the race to replace Johann Lamont, who resigned on Friday with an attack on UK Labour colleagues whom she accused of treating Scotland as a “branch office”.
Mr Murphy has said he will stand for a seat in the Scottish Parliament in 2016, if not before, and is running with a view to becoming first minister.
The shadow international development secretary told BBC News he is confident he can turn around the party’s fortunes in Scotland.
He said: “I’m not interested in left-wing Labour or right-wing Labour, or old Labour or new Labour. I’m interested in losing Labour.
“I want to end that period of losing Labour here in Scotland, starting with the UK general election in 2015, where I’m confident we can hold all the seats we currently have but pick up one or two on top and also win that election in 2016 for the Scottish Parliament.”
Pledging to unite the party, Mr Murphy said: “There is so much that has to change about the Labour Party and so much that has to change about our country. I’m determined to bring the Labour Party together, end the period of self harm that we’ve had in the Scottish Labour Party and get on and improve our country.”
Mr Murphy played a key role for Better Together during the referendum campaign when he carried out his pro-union 100 Streets in 100 Days tour. Former prime minister Gordon Brown ruled himself out of the running in the leadership contest but Mr Murphy plans to meet him to discuss further devolution for the Scottish Parliament.
His comments cam as a new poll showed Labour would be headed for a wipe out in Scotland if a general election were held tomorrow. The party would be left with just four seats in Scotland in the Ipsos Mori poll for STV News, which also found that 52 per cent of Scots would vote for the SNP if there was a Westminster election tomorrow.