Taking to her Instagram page on Tuesday, the mother-of-two uploaded a cute family picture of the American director posing with their sons.
"Happy Birthday to this one!! @lievschreiber," she wrote in the caption alongside a few emojis of a birthday cake and a balloon.
Liev, who turned 49, was seen smiling as he held his boys, Alexander, nine, and Samuel Kai, seven, in his arms during a family outing, in what appeared to be New York City.
Last Monday, the Hollywood stars announced they called time on their 11-year relationship in a joint statement, but revealed they remain on amicable terms for the sake of their children.
"Over the past few months we’ve come to the conclusion that the best way forward for us as a family is to separate as a couple," read the statement, reported by Entertainment Tonight.
"It is with great love, respect and friendship in our hearts that we look forward to raising our children together and exploring this new phase of our relationship."
Naomi Watts wished ex Liev Schreiber a Happy Birthday by posting a sweet family picture on Tuesday
They added: "While we appreciate your curiosity and support, we ask the press to be mindful of our children and respect their right to privacy."
One day after the announcement, Liev wished his former partner happy birthday in a comment on a photo she shared on Instagram. In the caption, he reportedly said, "Happy Birthday Sweetheart".
Though the couple never married, they have been together since 2005. The pair’s last red carpet appearance together at the Toronto Film Festival last month, where they attended the premiere of The Bleeder.
The news of the split comes soon after Naomi opened about her long-term romance with her beau in the spring fashion forward issue of Los Angeles Confidential.
The Hollywood stars announced they called time on their 11-year relationship a week ago
"Relationships are hard whether you're famous or not," she confessed. "I don't know anyone who doesn't have to work on it. Being an actor doesn't change anything."
"I'm sure it's the same if you're a doctor or a couple of lawyers," she added. "You have high-pressure jobs, lots of hours, stresses that come unexpectedly - and you have to figure out how to be present in the midst of it all."
Naomi and Liev have starred in three films together, with the latest - The Bleeder - set to be released later this year. They also starred together in the 2006 drama The Painted Veil as well as Movie 43, an anthology comedy.