Human rights lawyer, Sir Keir Starmer, beat rivals Rebecca Long-Bailey and Lisa Nandy after the first round of voting.
It marks a significant change of direction for the party, with a move away from the politics of Jeremy Corbyn and Ed Miliband who led Labour over the last decade.
His victory came after the planned special conference to unveil the winner had to be shelved because of the coronavirus crisis.
Angela Rayner won the deputy leadership race.
