Mr Duncan Smith, who led the Conservatives between September 2001 and November 2003, was awarded the accolade in the New Year Honours list.
He is the highest-profile political figure to be recognised and receives the honour for political and public service.
But a petition was launched in protest of his knighthood two days ago amid claims the honour was “an insult to the hundreds of thousands of vulnerable individuals across the country who are suffering as a result of his policies.”
In just 48 hours, the change.org petition, launched by NHS psychiatrist Mona Kamal, has nearly reached its target of 200,000 signatures.
Ms Kamal wrote: “During his time as Secretary of State for Work and Pensions Iain Duncan Smith was responsible for some of the cruellest most extreme welfare reforms this country has ever seen.”
She continued to reference the UK facing a UN enquiry into human rights abuses against disabled people during Mr Duncan Smith’s tenure at the Department of Work and Pensions.
“The suffering and impoverishment which are a direct result of the welfare reforms he has implemented are now undeniable,” she said.
Ms Kamal also attacked Work Capability Assessments for prompting panic attacks, anxiety and depression as well as Universal Credit and austerity.
“The fact that Iain Duncan Smith the individual responsible and the architect of such misery, is to receive the honour of a knighthood is an insult to the hundreds of thousands of vulnerable individuals across this country who are suffering as a result of his policies,” she wrote.
It comes after Mr Smith held on to his Chingford and Woodgreen seat during December’s election vote, securing 23,481 votes.
As well as his stint leading the Conservatives, he has held several high-profile roles. As work and pensions secretary under David Cameron, he was the architect of the Government’s controversial Universal Credit welfare reforms.
An ardent Brexiteer, he was a leading backbencher in the Tory European Research Group, which proved to be a thorn in the side of Theresa May.
Opposition parties have said it “beggared belief” that someone whose policies had caused so much distress should be honoured in this way.
Labour’s Lisa Nandy lambasted the award, tweeting it was a “disgraceful decision by Boris Johnson to reward a legacy of cruelty and failure”.
A Labour Party spokesman said it was “unfortunate to see that one of Boris Johnson’s first priorities” was to grant a knighthood to the “primary architect of the cruel Universal Credit system, which has pushed thousands of people into poverty”.
On Sunday, Mr Duncan Smith also slammed the online publication of more than 1,000 addresses of New Year Honours recipients as a “complete disaster”.
He told the Sunday Times that “very serious questions” needed to be asked about how the addresses were published online.