Mr Duncan Smith is planning to be among what organisers predict will be the one million protestors on the Liberty and Livelihoods countryside march next month.
He made his new pledge as he visited the Buckinghamshire County Show in Aylesbury on Thursday.
"If there was to be an outright ban, an incoming Conservative government would make time to repeal any illiberal legislation," said Mr Duncan Smith.
Ministers are currently continuing six months of consultation, which was announced in March, over the hunting issue.
Route to a ban?
Rural Affairs Minister Alun Michael Mr Michael has said the government wants to find "common ground" but will use the Parliament Act to force through the new plans if they met obstruction in the Lords.
The government will also let MPs get their way over lords' wishes if the House of Commons changed ministers' plans so there were no exceptions to a ban, says Mr Michael.
The Conservative leader's latest comments have been welcomed by the pro-hunting Countryside Alliance.
A spokesman for the campaign group said: "We are not planning for hunting to be banned, but we are encouraged by his commitment to, and support for, what is an integral part of the social fabric and economic life of the countryside.
"This is not an issue of right and left, it is an issue of right and wrong - and banning hunting is wrong."
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