The MPs are not launching a new political party – they will sit in Parliament as the Independent group.
But Chuka Umunna said they had “taken the first step” and urged other Labour MPs – and members of other parties – to join them in “building a new politics”.
“Politics is broken, it doesn’t have to be this way. Let’s change it,” he said at a launch event in central London .
Each of the seven took turns to explain their personal reasons for quitting the party.
Ms Berger said: “This morning we have all now resigned from the Labour Party. This has been a very difficult, painful, but necessary decision.
“We represent different parts of the country, we are of different backgrounds, we were born of different generations, but we all share the same values.
Chris Leslie said Labour had been “hijacked” by the far left.
He added that it was “increasingly clear that prominent figures in the Corbyn Labour leadership do not want to stop Brexit”.
In a statement, Mr Corbyn said: “I am disappointed that these MPs have felt unable to continue to work together for the Labour policies that inspired millions at the last election and saw us increase our vote by the largest share since 1945.
“Labour won people over on a programme for the many not the few – redistributing wealth and power, taking vital resources into public ownership, investing in every region and nation, and tackling climate change.
“The Conservative government is bungling Brexit, while Labour has set out a unifying and credible plan.