"The Good Wife" star Mamie Gummer is now an estranged wife ... because she just pulled the plug on her marriage.

Meryl Streep's oldest daughter beelined it to court Thursday and filed to divorce her husband Mehar Sethi after 6 years of marriage.

In the divorce docs, obtained by TMZ, Mamie lists the date of separation as May 6, 2023 ... and she's going with the boilerplate irreconcilable differences as the reason for the split.

Mamie is seeking joint legal and physical custody of their 5-year-old son Peter and 3-year-old daughter Mary.

She's also seeking spousal support and checked the box to terminate the court's ability to award support to her estranged husband.

Mamie and Mehar, a writer, tied the knot in February 2019 ... and, two weeks later she gave birth to their first child.

This is Mamie's second divorce ... her first marriage was to actor Benjamin Walker.

Meryl and Don Gummer announced their separation in September 2023 ... and in March 2020, Mamie's sister Grace Gummer filed for divorce from her husband.

Things happen in 3s!!!