Hilary Benn's speech making the case for air strikes in Syria was like Tony Blair's 2003 Iraq war speech, shadow chancellor John McDonnell has said.
Mr Benn's impassioned appeal to Labour MPs to vote with the government was an "excellent" piece of oratory, said Mr McDonnell.
But he added: "The greatest oratory can lead us to the greatest mistakes."
Mr McDonnell denied Labour was split and leader Jeremy Corbyn weakened by his defeat in Wednesday night's vote.
He said Mr Corbyn's decision to give MPs a free vote - rather than forcing them to back his position - was a "breakthrough for our politics in this country" as it had taken the issue of war "out of the political arena".
Shadow foreign secretary Hilary Benn, son of Mr Corbyn's political mentor Tony Benn, made a direct appeal to Labour MPs to support air strikes to combat the "fascists" of so-called Islamic State.
His speech was greeted with applause by Conservative MPs and some on the Labour benches - but Mr Corbyn, who had earlier made a speech of his own saying David Cameron's case for war "did not stack up", sat in silence.
Mr McDonnell, one of Mr Corbyn's closest allies, who also opposed air strikes, said Mr Benn's speech was typical of the high standard of Commons speeches on both sides during the debate.
He told BBC Radio 4's Today programme: "His oratory was great. He reminded me of Tony Blair's speech taking us into the Iraq war and I am always anxious that the greatest oratory can lead us to the greatest mistakes as well."
He dismissed the 66 Labour MPs who voted with the government as a "small minority" and said Mr Corbyn had the backing of the majority of Labour members, the party's national executive and the shadow cabinet.
He also condemned the abuse directed at Labour MPs who backed military action.
"We have said if they are Labour Party members we have disciplinary processes and they will take place. We cannot have intimidation in our party," he told Today.
Shadow Commons leader Chris Bryant said some of the abuse directed at MPs over the Syria vote had been "beyond the pale" and called for a review of the security arrangements for MPs' homes and offices.
He said it was a "fundamental principle" that MPs should be free to speak and vote "without fear or favour" or intimidation.
Commons Leader Chris Grayling said MPs' security arrangements "is and will be continuing as a priority" for the Commons' authorities.
Some Labour MPs claim to have been sent pictures of dead babies by anti-war protesters and others have been branded warmongers and "red Tories".
Walthamstow MP Stella Creasy, whose office was the target of anti-war protests, complained of intimidation while considering how to vote in Wednesday's debate.
Mr McDonnell denied claims there were efforts to deselect Ms Creasy, saying: "There is no way she should be de-selected, she is an excellent MP, she has my support."
'Not robust enough'
Campaign group Stop the War, which until recently was chaired by Mr Corbyn, hit back at claims its supporters were bullying Labour MPs on social media, and said it would continue to support the Labour leader "in every way that we can".
In a joint statement, Stop the War chairman Andrew Murray and Convenor Lindsey German said: "Stop the War condemns the whining complaints from those MPs who apparently do not like being lobbied.
"If an MP is not robust enough to withstand emails and tweets, they should really not be voting for bombing other people - those who wish to be alone with their consciences would do better to consider a life of religious contemplation.
"Stop the War will continue to hold to democratic account all those MPs who vote for war."
Former London mayor Ken Livingstone, who is co-chairing Labour's defence review, has meanwhile suggested there might be "a few" de-selections of sitting Labour MPs.
He told LBC radio: "If I had an MP who had voted to bomb Syria then I would be prepared to support someone challenge him as long as they were good on a load of other issues."
Mr Livingstone said the 2020 intake of Labour MPs would be "massively" pro Corbyn.