Former "Family Ties" star Meredith Baxter -- who played the mom Elyse on the 80s sitcom -- is now this much closer to tying the knot with her longtime girlfriend ... TMZ has learned, she just got her marriage license.

Sources tell us, Meredith and gf Nancy went to the Beverly Hills courthouse Friday to get the official paperwork to pave the way for their upcoming nuptials.

The wedding date (and wedding details) haven't been announced, but the invites have already been sent to guests -- so it's definitely happening.

FYI, Meredith announced she was a lesbian in 2009 -- after three failed marriages to men.