"We have mutually decided to end our marriage. We'll always be family and continue to cherish our relationship based on the special love, integrity, and respect we have always enjoyed," the estranged couple said in an exclusive joint statement to People.com.
No reason was given for the split.
Gilbert, 48, is best known for her work on TV's "Little House on the Prairie." She also recently competed on "Dancing with the Stars."
Busfield, 55, is a former cast member of the small-screen dramas "Thirtysomething," "The West Wing" and "Studio 60 on the Sunset Strip."
"They are engaged and both are incredibly happy," Gilbert's representative told People.com.
An insider told the celebrity magazine the couple got engaged during the holidays.
The report did not say where or when the pair intend to wed.
Gilbert was previously married to actors Bo Brinkman and Bruce Boxleitner.
Busfield has also been married twice.
'GIRL MEETS WORLD:' Rowan Blanchard, an 11-year-old actress from Los Angeles, has been cast in the "Boy Meets World" spinoff, "Girl Meets World," producers said.
Blanchard has appeared in the films "Spy Kids: All the Time in World in 4D" and "The Back-up Plan."
She has been hired to play Riley, the daughter of Ben Savage's Cory and Danielle Fishel's Topanga, in the upcoming Disney Channel show after a nationwide casting search, EW.com reported Monday.
"As soon as Rowan walked into the room, I was reminded of why Ben Savage was loved as Cory Matthews," Michael Jacobs, who is producing the "Girl Meets World" pilot, told EW.com. "Rowan is real and accessible and I am hopeful this girl is about to meet a world that will love growing up with her as well."
The pilot is to start shooting next month.
TAYLOR SWIFT: Diet Coke says U.S. country music star Taylor Swift has signed on to star in its new advertising campaign.
"Taylor's unmatched business savvy, talent and drive to succeed are an inspiration to everyone. She's an extraordinary individual and a wonderful symbol of achievement," Katie Bayne, president of North America brands for The Coca-Cola Co., said in a statement Monday. "Taylor tells us that every day Diet Coke plays a small part in helping her stay extraordinary. It's one of the many reasons she's the ideal partner to represent our brand."
"I've said for years that Diet Coke just 'gets me' and my lifestyle. I'm so excited about our new partnership," said Swift.