Graham explained why Winfrey would make a good president -- even though the TV personality has said she won't run against President Donald Trump in the 2020 election.
"You can trust her, number one," he told host Ellen DeGeneres. "She's smart. She has a photographic memory. She works very, very hard. She has qualifications to do it. And she's very successful."
Winfrey said in the March 2018 issue of InStyle that a presidential run is not for her.
"I've always felt very secure and confident with myself in knowing what I could do and what I could not do. And so it's not something that interests me. I don't have the DNA for it," she said.
Graham and Winfrey have been together over 30 years. Graham said one key to their successful relationship is his comfort with Winfrey's success and happiness with his own pursuits.
"The thing about our relationship is I want the best for her. I'm dedicated to her happiness, so that's great for her. I want her to be the best she can possibly be, and she's done a pretty good job of doing it," the author said.
"For me, I've been able to find my own happiness and to find my own skills, my own talents, my own abilities. I'm satisfied with that. I'm happy with that," he added. "So the combination, when you have a good partner that's able to self-actualize their potential and you're able to self-actualize yours? You know, one and one equals about six."
Graham and Winfrey were engaged at one point but have not married. Winfrey said in the September 2017 issue of Vogue that marrying Graham would have ended in divorce.
"We would not have stayed together, because marriage requires a different way of being in this world," she said. "His interpretation of what it means to be a husband and what it would mean for me to be a wife would have been pretty traditional, and I would not have been able to fit into that."