"We are so thrilled to announce our engagement," a representative for the couple told PEOPLE. "We can't wait to celebrate with our friends and family, including our second family at Once Upon a Time."
31-year-old Josh, who was previously married to Sherlock actress Lara Pulver, proposed in LA on Wednesday much to the delight of his 35-year-old bride-to-be.
The duo met on the set of ABC's fantasy show, which sees Ginnifer star as Snow White and Josh take on the role of Prince Charming, in 2011.
"It hit me like a blinding light," said Josh about first seeing Ginnifer. "I thought, 'I'm in trouble now.'
"It's definitely a plus that we get to spend so much time together," added Josh. "I think it adds something; it adds a different dynamic to the characters that we're playing that we can bring to it."
Despite their obvious chemistry the couple's co-star Lana Parilla has said that they are professional on set.
"They're great. They're total pros, they really are," said Lana. "We all know they're together, but when they're on set, they're very professional."
Ginnifer's impending union with Josh will be her first marriage although she was previously engaged to Cabin Fever actor Joey Kern and was in a long term relationship with Katie Holmes' ex-fiancé Chris Klein.