The FlashForward star and his wife Maria Dolores Dieguez welcomed their first child on Monday.
However, Fiennes admitted that he is exhausted after dealing with a newborn baby.
"I'm on my knees," he told The Mirror. "It's a beautiful experience, the best experience of my life. It puts everything in perspective."
Fiennes added that he will be shooting the finale of FlashForward in a few days so will be returning to work straight away.
"I did a little bit of theatre, and I thought that was tough, eight shows a week for six months," he said. "But I have to say, TV sorts the men from the boys - tough schedule... and now the sleep deprivation as a consequence doesn't help!"
FlashForward resumes its first season on March 18 on ABC in the US and on March 22 on Five in the UK.