The actress, 47, discussed her friendship with Martin, her ex-husband and a singer for Coldplay, and Johnson, also an actress, in the February issue of Harper's Bazaar.
Paltrow and Martin, 42, split in March 2014 after 10 years of marriage and have two children, Apple, 15, and Moses, 13. In the interview, Paltrow explained how welcoming Johnson makes for a more full life.
"I love her," Paltrow said of Johnson, 30. "I can see how it would seem weird because it's sort of unconventional. But I think, in this case, just having passed through it iteratively, I just adore her."
"I always start to think of the ampersand sign -- what else can you bring in, instead of being resistant to or being made insecure by? There's so much juice in leaning in to something like that," she added.
Paltrow and her husband, Brad Falchuk, have spent holidays with Martin and Johnson, who were first linked in October 2017. Paltrow said her dynamic with Martin continues to evolve, nearly six years after they "consciously uncoupled."
"It's not like there's a finish line," the star said. "It's a lifelong commitment to constantly reinvent your relationship with your ex, which you do presumably because you have children together. I don't see a reason to do it if you don't have children together. Some people do."
"But I think we put all the hard work in at the beginning," she added. "I would say rarely is it difficult now. We've learned how to communicate with each other. We love each other. We laugh. We have the best of each other. It's really nice. It makes you feel like you don't have to lose."
Paltrow made headlines in October after wishing Johnson a happy birthday on Instagram.
"Happy 30th birthday to this absolute gem," she wrote.
Paltrow told Harper's Bazaar she's also friendly with her ex-boyfriend Tony Woods and her ex-fiancé, actor Brad Pitt.
"I don't have any really bad blood," she said.
Paltrow most recently appeared in the film Avengers: Endgame and will star in a new Netflix series, The Goop Lab. The show follows Paltrow and her Goop team as they explore different wellness topics and premieres Jan. 24.