Mr Reed, the current leader of Lambeth Borough Council, dedicated his win to his late predecessor Mr Wicks, pledging to carry on his work, and attacked David Cameron and London Mayor Boris Johnson in his acceptance speech.
– Steve Reed, leader of Lambeth Borough Council
Tonight the people of Croydon North sent a clear message to David Cameron," he said.
He cannot be the one-nation prime minister Britain needs if he stands by doing nothing while Croydon faces one of the highest levels of youth unemployment in London.
He cannot be the one-nation prime minister Britain needs if he is giving tax cuts to millionaires while pensioners here in Croydon are left to pay more.
David Cameron needs to listen. People are hurting because his economic policies are not working. He must change course on the economy.
Labour retained the constituency of Croydon North in a Westminster by-election today, romping home by a margin of almost 12,000 votes.
The party's candidate Steve Reed secured 15,898 votes and a massive 47.9% margin of victory, up from the 31.9% recorded at the 2010 general election by former minister Malcolm Wicks, whose death in September triggered the poll.
Conservatives took second place, with their candidate Andy Stranack receiving 4,137 votes, but Liberal Democrat Marisha Ray came fourth behind the UK Independence Party and lost her deposit.
Voters go to the polls in less than two hours to decide who will be the next MP for Croydon North.
There are 12 candidates. Labour had a comfortable majority in this seat at the 2010 general election.
The by-election comes after the death of MP Malcolm Wicks, who lost his battle with cancer in September, aged 65.
He had been an MP for Croydon North for two decades and held the seat with a 16,483 majority.