Set on the eve of the 2008 financial crisis, the film follows staff over a 24-hour period at a firm that is about to go under.
Speaking at the movie's premiere in London's Vue Leicester Square, Irons revealed: "Because my father was a chartered accountant, I'm an actor, and I'm hopeless with money.
"I'm not really interested in it. It's very nice to have some, but I have no interest in it as long as I have enough to buy a cup of tea. So in a way, I reacted against my father."
Written and directed by JC Chandor - the son of a stockbroker - the film boasts an all-star cast including Kevin Spacey, Paul Bettany, Demi Moore and Stanley Tucci.
Oscar-winner Irons said his CEO character was "very pragmatic".
"He's a man who finds himself in the situation and has to deal with it. He has to try and keep the firm afloat, which is what he does, and I suspect there are a lot of people, both in this country and overseas, who are trying to do just that," he added.
"I don't think it's my job for the character to question it, the ethics of using paper money, computer money really, to make more money. But I personally think that is wrong - you don't buy money to make more money, and I think there's a little bit of truth in that."
The film's US release date last October coincided with the Occupy Wall Street protests. "They couldn't have planned it better, the release of the movie," Irons' co-star Paul Bettany said.
Margin Call is in UK cinemas on January 13. Here are the stars out in force for last night's London premiere: