Rebecca Long-Bailey says Labour MPs will face automatic reselection if she becomes leader
Labour MPs would have to face automatic reselection before every general election if Rebecca Long-Bailey becomes leader.
The Shadow Business Secretary said she wanted to "throw open the door to a new generation" of Labour politicians.
Ms Long-Bailey's support for "open selections" will prove controversial with many sittings MPs, who say they are a distraction from trying to defeat the Conservatives.
But it will prove popular with Labour members, who say the current system is undemocratic and allows some MPs to have a seat for life, regardless of their performance.
Addressing a ralling in London on Tuesday, Ms Long-Bailey said she wanted to have "a frank conversation with our movement about where we go next".
She said: "We need to rip up our outdated rule book that has held back our members for too long and throw open the door to a new generation of MPs and candidates.
"Being an MP or elected representative is a privilege that must be earned, and I want to open the discussion now on how our candidates should be selected, how we nurture and bring through talent in our movement, whilst recognising and valuing the experience of sitting MP’s.
"We all know that person. That talented, selfless and hardworking person who’d make a brilliant MP but would never dream of putting themselves forward. It’s those people I want to raise up.
"The collective knowledge and experience of our movement is Labour’s greatest strength. Now is the time to unleash it. And that’s why I support open selections for parliamentary candidates. We need a democratic revolution - both in the country and in our party."
At the moment, Labour MPs can face a "trigger ballot" if at least one-third of local branches in their seat demand they face reselection.
Under the proposed changes, a reselection process must take place, with the sitting MP one of the candidates unless they decide to stand down or retire.
The policy announcement will further cement Ms Long-Bailey's reputation as the Corbynite candidate in the Labour leadership race.
Her place in the final round of the contest is likely to be confirmed on Friday when Unite announces who it is endorsing.
Bookies' favourite Sir Keir Starmer is already on the ballot paper, while Lisa Nandy's hopes of joining him received a huge boost when the GMB said it was backing her.
Jess Phillips announced on Tuesday that she is quitting the race, while Emily Thornberry faces an uphill battle to get the required number of Constituency Labour Party endorsements to make it through.