"I feel like I have a true partner," said Williams at his birthday party in New York City on Wednesday night, People Magazine reported.
Williams and Fowler mat a year and a half ago in Florida.
He made the proposal to Fowler, an American Airlines flight attendant, at New York restaurant "Tavern on the Green" with both of their families looking on.
This will be the third marriage for Williams, who has two children from each of his previous marriages.
Celebrity Families of 2014 [PHOTOS]