"The people of Liverpool have spoken decisively in favour of the Labour Party.
"They have rejected the Conservatives and Liberal Democrats within this city and have given me their trust and the Labour Party their trust.
"I promise to you that we will deliver on our pledges and on our promises."
Labour's Ian Stewart has become Salford's first elected mayor after a second round of voting.
Voters have chosen the current council leader Joe Anderson as Liverpool's first mayor. He won the election with 54% of the vote.
Voters in Manchester voted against having an elected mayor in a referendum.