American publication TMZ reports that Johnny, 39, packed his bags and moved out of Courteney's home in Los Angeles shortly before Thanksgiving. The Snow Patrol guitarist is believed to be back in the UK.
Sources say the pair attended counselling to try and work out their issues, but they mutually decided to end their relationship.
Courteney Cox and Johnny McDaid split just before Thanksgiving
The report went on to say that Courteney and Johnny differed on their lifestyle choices. While the former Friends star, 51, liked to go out on the town, her fiancé was more private and liked to stay out of the limelight.
The couple were last pictured in public together in August.
Johnny proposed to his actress love last year during a romantic getaway to Turks and Caicos to celebrate Courteney's 50th birthday.
The Snow Patrol rocker proposed during a romantic getaway for Courteney's 50th
In June the pair confirmed their engagement on Twitter and shared their happy news simultaneously with a selfie. The actress captioned it, "I'm engaged to him", while Johnny wrote, "I'm engaged to her."
The ring was designed by Jennifer Meyer, wife of Tobey Maguire.
The couple were said to be scouting for wedding venues in Johnny's native Northern Ireland, and Courteney's close friend Ed Sheeran was even tipped to perform at the nuptials. The Thinking Out Loud singer was the one who initially introduced the lovebirds.
"We're certainly grateful to Ed for introducing us," Courteney told The Sun in August. "I can't imagine him not playing something at the wedding."
Ed Sheeran, who was tipped to perform at the wedding, introduced the couple
Earlier this year the actress also revealed that her 11-year-old daughter Coco, who she shares with her ex-husband David Arquette, was heavily involved in the wedding planning and wanted to act as the maid of honour.
This would have been Courteney's second wedding. Her ex David married celebrity reporter Christina McLarty in April, a year after welcoming their son Charlie.