The BBC reports:
Deputy Prime Minister and Lib Dem leader Nick Clegg said: "I genuinely believe that we will look back on today as a landmark for equality in Britain.
"Tonight's vote shows Parliament is very strongly in favour of equal marriage.
"No matter who you are and who you love, we are all equal. Marriage is about love and commitment, and it should no longer be denied to people just because they are gay.
"The Liberal Democrats have long fought for equal marriage. It is party policy and I am proud that the Liberal Democrats are part of the coalition government that are making it happen."
MPs were given a free vote on the bill, meaning they were not ordered to vote for or against by party whips.
Their decision to back the bill at second reading signifies that they approve of it in principle. The legislation will now receive more detailed parliamentary scrutiny.Rule, Brittannia!