Transport Secretary Patrick McLoughlin officially launched the contest to run inter-city services on the line, which runs from London Kings Cross to Edinburgh via the North East.
He said: “Services along the East Coast Main Line are set to be transformed over the coming years through £240m-worth of investment which will improve reliability and boost capacity for passengers and freight.”
But Labour warned that handing the line over to a private firm would simply mean that profits went to the operator rather than the Treasury.
Grahame Morris, Labour MP for Easington, said the entire rail network should be bought back into public ownership, adding: “This government is being driven by ideology rather than what is best for travellers, employees and tax payers.”
The winning bidder will initially be required to offer at least 32 services a day from Newcastle to Kings Cross between Monday and Friday.
But from May 2020 onwards, the minimum requirement will be 45 services from each weekday.
This will follow the introduction in 2019 of new state-of-the-art trains, called the class 800 series, to replace aging inter-city trains first introduced in the 1970s, as part of a £5.8bn programme to upgrade stock on the Great Western and East Coast Main Lines.
However, Labour critics argue that this investment and improvements in the service could also have taken place if the franchise was left in public hands.
The East Coast franchise has been run by the government-owned Directly Operated Railways since previous operator National Express gave up the franchise in November 2009.
And it has been profitable, returning £208m in premium and dividend payments to the Treasury in the previous financial year.
Three firms are in the running to take over the franchise. They include a consortium of Keolis, a French firm which is majority owned by SNCF, France’s national state-owned railway company, and Eurostar, which is once again majority-owned by SNCF.
The other bidders include East Coast Trains Ltd, a business owned by First Group Plc, and Inter City Railways Limited, which is owned by Stagecoach Transport Holdings Limited and Virgin Holdings Limited.
The successful bidder will be announced in November with the new franchise beginning in March 2015 and running for eight years, with the Government able to extend it for a further year if it wishes.
Rail Minister Stephen Hammond said: “Franchising has been a force for good for our railways, delivering record growth to an industry that was once in decline.”
But Mary Creagh MP, Shadow Secretary of State for Transport, said: “East Coast is working well and will have returned £800m to the taxpayer by the end of this financial year. David Cameron should tackle his Government’s cost-of-living crisis and cap rail-fare rises for struggling commuters instead of obsessing about handing East Coast over to the private sector.”