Jens Martin Gammelby (born 5 February 1995) is a Danish professional footballer who plays as a right-back for Danish Superliga club Silkeborg.
A Silkeborg academy graduate, Gammelby made more than 100 first-team appearances and scored nine goals in his initial spell before a 2018 transfer to Brøndby. He later had loans at Lyngby and Miedź Legnica in Poland, and spent 2023 with Norwegian side HamKam. In January 2024, he returned to Silkeborg, winning the 2023–24 Danish Cup with the club.
Gammelby has also been capped by the Denmark League XI, scoring on his debut in 2018.
