The couple appear to have been consulted as they are "intimately familiar" with the challenges of "walking away from a role that has defined them".
The Duke and Duchess of Sussex quit as working members of the royal family in January 2020 to move to America and raise their family.
Meghan added about Williams on her new podcast: "The three of us really know that sometimes the right decision isn't the easiest decision.
"It's the hard decision. And it takes a lot of thought and a lot of counsel and a lot of support to just go, 'uh, uh, uh' and then just make the choice."
Mum-of-one Williams said the decision to walk away from tennis was a challenge as it has been the "one thing" defining her life.
She added: "The worst place to be is on the fence, as you know. So, it's like, 'Make a decision: either be in it or be out of it'. And I was on the fence for a while because I love what I do."
Williams is to compete in her final US Open this week, and said she sent the Sussexes a preview of the Vogue article in which she announced her decision to retire.
She added: "I wanted you to understand what it meant to have your support and for H's support – for everything.
"I've been doing this my entire existence. Even before I was born, it was what I was meant to do and what I was supposed to do and what was chosen for me."
Meghan also used the podcast to reveal how she felt forced into continuing with royal engagements on a tour of South Africa despite being left in tears when her son Archie's nursery was hit by a fire.
She also said she felt the "negative" aspects of being viewed as ambitious when she joined the royals.
