Taking to her Stories, the star shared a collage that featured many of the programme's best-known panellists, including herself, which she re-posted from the Loose Women Instagram account.
A caption read: "Happy 21st Birthday Loose Women."
The 60-year-old appeared on the show in its first series back in 1999, and has made many appearances since, with her then-baby son Jack even making his on-screen debut on the show in 2002.
Ruth now balances her work on the programme with presenting This Morning with her husband, Eamonn Holmes, on Fridays and during school holidays.
WATCH: Ruth Langsford shows off incredibly tidy home - and we're envious!
The couple have had several reasons to celebrate this year, even despite the pandemic. A few weeks before lockdown, their son turned 18 and the family enjoyed a spectacular party at their home in Surrey.
Over the summer, Eamonn and Ruth celebrated ten years of marriage, having tied the knot on 26 June 2010 after a long romance.
Ruth has starred on the long-running show since 1999
The former GMTV host surprised his wife with a gorgeous cake and balloons, which Ruth shared photos of on Instagram, alongside the caption: "What a wonderful romantic you are @eamonnholmes #anniversary."
Recently, however, the former Strictly star admitted that everything isn't always rosy between her and her husband.
Speaking to Prima magazine, Ruth said: "There are times when he really annoys me and I really annoy him and there are times when I think, 'Get out of my face."
"Obviously, you're not always going to get on, but you have to make it work. Underneath it all, we know we have a strong relationship."
Explaining that they've mostly been very happy over the last 23 years of their relationship, Ruth added: "Eamonn and I can have big rows and argue, then ten minutes later we're laughing about something."
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