The 23-year-old made 14 league appearances for the Royals last season after moving to the Madejski Stadium from Watford.
Bond has been capped by England at Under-20 and Under-21 level, having previously represented Wales at youth international level.
He becomes Gillingham's 11th signing of the summer transfer window.
Find all the latest football transfers on our dedicated page.
League One side Gillingham have signed Reading goalkeeper Jonathan Bond on loan until 7 January 2017.