Which of Henry VIII's six marriages lasted longest?

Katherine of Aragon! Married: 1509 - 1533. Katherine Parr was the next longest marriage at only 4 years. It may have lasted longer if Henry had not died. His shortest marriage was to his beloved sister, Anne of Cleves. Apparently, she resembled a horse...but she did keep her head!

Henry VIII’s longest marriage was to Katherine of Aragon, daughter of King Ferdinand and Queen Isabella of Spain. Eight years before her marriage to Henry in 1509, Katherine was married to Henry’s elder brother, Arthur, who died of sickness at just 15 years old.

Together, Henry and Katherine had a daughter, Mary Tudor, who was born at Greenwich Palace, but Henry wanted a son. Frustrated at Katherine’s perceived inability to produce a male heir and now in love with one of Katherine’s ladies-in-waiting, Henry declared their marriage nullified in 1533.

Henry claimed that since his wife had previously married his brother, the marriage was invalid. Katherine vigorously contested this charge, explaining that the marriage was never consummated. When the Pope refused the annulment, Henry VIII officially started his own church, the Church of England.

https://www.rmg.co.uk/stories/topics/who-were-henry-viiis-wives

1. Catherine of Aragon: 23 years, 11 months and 12 days (annulled)
2. Catherine Parr: 3 years, 6 months and 16 days (widowed)
3. Anne Boleyn: 3 years, 3 months and 19 days (annulled & executed)
4. Jane Seymour: 1 year, 4 months and 24 days (died)
5. Catherine Howard: 1 year, 3 months and 26 days (executed)
6. Anne of Cleves: 6 months and 3 days (annulled)