Mrs May used an unscheduled announcement on Tuesday to confirm she will go to the House of Commons to seek permission to hold the vote on June 8.
Mr Duncan Smith backed Mrs May to return from the election with an even stronger mandate to negotiate Britain’s path out of the European Union.
Speaking on Sky News, he said: “I think when you examine her decision logically, it makes sense.
“I think Theresa May was right – I think she was reluctant to come to this decision, but I think she’s come to this decision on the evidence that has been presented to us by the behaviour of the Lords and some of the other parties.
Theresa May's decision to hold an early election was praised by Iain Duncan Smith
She’s come to this decision on the evidence that has been presented to us by the behaviour of the Lords
Iain Duncan Smith
“We have the biggest decision taken by the British people to leave the European Union. We have to deliver on that, which requires us to get a big bill through Parliament – which will be very difficult – and also negotiate in strength with the European Union to get the best deal we can.”
Mr Duncan Smith said a Conservative victory will give the Prime Minister a post-Brexit mandate to fulfil the wishes of the British people.
Mrs May had always insisted she would not call a snap election, but her Conservative colleague believes her hands were forced because of challenges to Brexit.
“You could see how one four-line bill was delayed to a degree in the Lords,” Mr Duncan Smith added.
“They made it very clear they would go on doing that when the big bill came. Also, it is time now to have an election because the negotiations are about to start.”
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Responding to questions on the difficulties posed by Remainers to the Prime Minister, he said: “She would have got bogged down, it was quite clear they were threatening that.
“They kept saying, the Liberals have said, Labour have said and Peers have said, ‘You don’t have a mandate,’ so, in a sense they have asked for this election.”
Addressing the nation, Mrs May said her Cabinet has believed it was the right time for a general election to be called.
She said: “I have just chaired a meeting of the Cabinet, where we agreed that the Government should call a general election, to be held on June 8.
Politicians react as Theresa May calls snap general election on June 8 Tue, April 18, 2017
UK Prime Minister Theresa May has announced her intention to hold an early general election on June 8
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Theresa May has called for a snap general election
“I want to explain the reasons for that decision, what will happen next and the choice facing the British people when you come to vote in this election.
“Last summer, after the country voted to leave the European Union, Britain needed certainty, stability and strong leadership and since I became Prime Minister The Government has delivered precisely that.
“Despite predictions of immediate financial and economic danger, since the referendum, we have seen consumer confidence remain high, record numbers of jobs and economic growth that has exceeded all expectations.”