Forward Miller and full-back Parter were both graduates of Gillingham's Academy system and regulars for the club's under-21 development side.
Miller made his first-team debut against Wycombe in November 2010 and enjoyed a total of six senior appearances, scoring once in a 4-3 defeat at home to Crewe in March 2012.
Parter, however, failed to appear for the Gills' first-team despite appearing in several pre-season friendlies.
Gillingham's official website read: "We would like to thank both lads and wish them every success in their future careers."
- Sports & Recreation