Hilary Benn received huge applause and cheers from all sides of the House of Commons following his speech in favour of carrying out airstrikes against so-called Islamic State in Syria.
Britain has a "moral and practical duty" to carry out airstrikes against IS in Syria, the shadow foreign secretary told MPs.
Mr Benn asked MPs whether they could stand aside and refuse to act fully, passing the responsibility for defending the UK's national security to other nations, when "we know they (IS) are plotting more attacks".
The Labour MP said: "I believe we have a moral and a practical duty to extend the action we are already taking in Iraq to Syria.
"We must now confront this evil. It is now time for us to do our bit in Syria."
Mr Benn said MPs should not "walk by on the other side" and must show solidarity with Britain's allies.
Foreign Secretary Philip Hammond praised Mr Benn's "outstanding" speech, saying it would "go down as one of the truly great speeches made in this House of Commons".
The shadow chancellor warned it could foster another generation of militants determined to commit a Paris-style terror attack.
The Defence Secretary has warned the RAF that the fight against Islamic State will not be short or simple.
Officers were posted outside the constituency office of Neil Coyle, the Labour MP for Bermondsey & Old Southwark.