The Smash star, 43, quietly separated from screenwriter Daniel Zelman last year (11) and reportedly moved on to date her TV co-star Will Chase, who ironically breaks up her TV marriage on hit drama Smash.
Messing and Zelman met in college in 1990 and have an eight-year-old son, named Roman. Messing has started legal proceedings in Los Angeles to finalise the split.
She has cited “irreconcilable differences” for the break-up and is requesting spousal and child support, according to court documents obtained by TMZ.com.
Messing has hired top celebrity lawyer Neal Hersh to represent her in court.
The actress recently opened up about the heartbreaking split, telling U.S. magazine Ladies Home Journal, “Twenty years. It’s a very long time.” And she attributed the couple’s move to New York, where she filmed Smash, for the split: “When I say the move to New York was traumatic, it was traumatic because every aspect of my life was going through a huge change.”