The actor plays Rodrigo Borgia - who became Pope Alexander VI - in the show and told Sky Magazine that it is more about the characters than the costumes and period details.
Irons said: "It's not a documentary, it's a great story. It's high drama and high stakes.
"I hope you will be inside the heads of these people and that the costumes will be the icing on the cake. But it's about the people, what they feel and why they do what they do."
Talking about the power wielded by the House of Borgia in the 1400s and 1500s, Irons added: "There are great parallels with modern power structures - whether it's Putin and the Kremlin, Berlusconi and Rome, or Bush and America.
"To get things done you often have to behave in a not very admirable way. The Vatican is a powerhouse with a lot of infighting, shuffling for power, and foreign policy. So, things haven't changed much."
The Borgias has already been renewed for a second season. It currently airs Sundays at 10/9c on Showtime and will debut in the UK on Sky Atlantic on August 30.
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Watch a behind-the-scenes video from The Borgias below: