The couple married on December 30 2011.
The actress and producer, 37, married Doctor Who star David Tennant, 50, on December 30 2011.
In an Instagram post she wrote: “The happiest day followed by the happiest life. Thanks DT. #tenwithten #niche.”
The photograph shows the couple hugging son Ty.
The award-winning actor can be seen looking down at Ty and smiling at him as his mother cradles his head.
David Tennant is wearing a suit and his wife is in a tiara and white chiffon dress with a veil.
The couple have five children – 19-year-old Ty, 10-year-old Olive, eight-year-old Wilfred, Doris, six, and Birdie, 21 months.
Tennant adopted his wife’s son Ty from a previous relationship.
The couple met in 2008 on the set of Doctor Who when Georgia Tennant played the Doctor’s genetically engineered daughter, Jenny.
The character was so popular that she was given her own audio spin-off, called Jenny, which was created by audio drama producer Big Finish.
Friends of the couple added comments underneath the post.
The author and presenter Giovanna Fletcher posted five red hearts, while the actress Isabella Pappas wished the couple a happy anniversary, followed by three hearts.