Scarlett Johansson on Being a New Mom: 'It's Wonderful and Exhausting'

— -- Scarlett Johansson took on a new role this year – female action hero. In “Lucy,” she played a woman powerful enough to destroy the world and in the blockbuster Marvel Comics movies, she played Black Widow. Those roles were a far cry from what she’s doing in her real life - taking care of her new baby.

In an interview with Barbara Walters for the two-hour ABC News special, "Barbara Walters Presents: The 10 Most Fascinating People of 2014," Johansson, 30, talked about becoming a mother with her new husband, French creative director Romain Dauriac.

"It's wonderful, and exhausting," Johansson said of having a child. "The love is just unbelievable. It's very overwhelming."

Johansson said she cares for her daughter herself, from changing diapers to breast-feeding.

"The whole bit," she said. "I'm nursing, and I love it, I love it. It's the best way to get back in shape."

Johansson, who will next star in the film "Avengers: Age of Ultran," scheduled to open in May, has been working as an actress since she was eight years old.

When not in front of the camera, Johansson tries to avoid the spotlight, and said she lives a "pretty low-key lifestyle." One exception to that was her marriage to actor Ryan Reynolds, which landed her first in the tabloids and then in divorce court, four years before she secretly married Dauriac.

"I think being in a committed relationship takes work... It's challenging, but when it works, it's really worth it," Johansson said.