MPs have approved the Budget after a week that saw one senior minister resign from the cabinet and a government U-turn on benefit cuts.
The Budget passed with a majority of 35 MPs at 310 votes for to 275 against.
Duncan Smith said in his resignation letter: "I am unable to watch passively whilst certain policies are enacted in order to meet the fiscal self imposed restraints that I believe are more and more perceived as distinctly political rather than in the national economic interest."
However, this week saw Duncan Smith's replacement Stephen Crabb confirm that the government had shelved the planned cutbacks.
Meanwhile, Duncan Smith voted in favour of the Budget this evening.
The Budget also contained bad news for fizzy drinks and confectionery companies, with the surprise introduction of a new sugar tax, and yet another shakeup of the pensions market, with the launch of a new Lifetime ISA.