"We are so thrilled to announce our engagement," they said in a statement. "We can't wait to celebrate with our friends and family, including our second family at Once Upon A Time."
Having met on the set of the hit TV show, Josh and Ginnifer went public with their romance in March 2012.
"It hit me like a blinding light," said Kentucky-born Josh of his first encounter with Ginnifer. "I thought, 'I'm in trouble now.'
"It's definitely a plus that we get to spend so much time together," he added of their joint work commitment. "I think it adds something; it adds a different dynamic to the characters that we're playing that we can bring to it."