The Shadow Home Secretary – one of Jeremy Corbyn's key allies – missed the second reading of the Bill last week due to illness.
But she turned up to the Commons tonight to back the triggering of Article 50.
Speaking after the vote, she warned Brexit will be "quite disastrous" but insisted Labour would hold the Government to account.
I think that a Tory Brexit is going to be quite disastrous
She said: "The shadow cabinet agreed this week that we would vote for the third reading of triggering Article 50 and I did that.
"I think that a Tory Brexit is going to be quite disastrous.
"I don't believe we've given a blank cheque, no. We're going to be holding them to account on the floor of the House."
Diane Abbott missed the second reading of the Brexit Bill last week
Theresa May mocked Mrs Abbott during a fiery edition of Prime Minister's Questions earlier today.
She said: "Perhaps members of the Labour Party are starting to realise that the only real headache is their leader."
The Hackney MP was accused of cowardice over the vote last week, with several MPs suggesting she should consider her position.
Theresa May mocked Abbott during Prime Minister's Questions
REMOANERS: These people hate BREXIT!
Mon, January 16, 2017
Remainers are finding it hard to accept Brexit.
1 of 14
Jeremy Corbyn imposed a three-line whip on Labour MPs
Shadow Business Secretary Clive Lewis, another Corbyn ally, resigned from the frontbench to vote against triggering Article 50.
He said: "When I became the MP for Norwich South, I promised my constituents I would be 'Norwich's voice in Westminster, not Westminster's voice in Norwich'.
"I therefore cannot, in all good conscience, vote for something I believe will ultimately harm the city I have the honour to represent, love and call home."