He has signed a contract until April 2011 and is their fifth boss in a year.
Chairman George Rolls told BBC Radio Solent: "We'll see a good, young, bright energetic manager who will bring something different to the table."
Earlier this month, previous Terras manager Ian Hutchinson and his assistant Andy Mason were sacked just days after agreeing new contracts until the end of the season.
He has a real tough challenge ahead down there but Jerry has never shied away from a challenge
Redditch chairman Ken Rae
The Terras had looked set to appoint Jimmy Quinn last week but they withdrew their contract offer late on.
Weymouth are bottom of the table and seven points adrift of safety.
Gill, who has been playing for Redditch this season, takes charge of his first game on Saturday as relegation rivals Lewes visit the Wessex Stadium.
Redditch chairman Ken Rae told his club website: "Jerry is a consummate professional who knows the game inside out and his experience will certainly help him at Weymouth.
"He has a real tough challenge ahead down there but Jerry has never shied away from a challenge throughout his career as a footballer and I am certain he will do well for them.
"Jerry goes with our blessing and best wishes and we have released him with immediate effect in order that he can link up with his new squad and take charge for Weymouth's relegation six-pointer this weekend at home to Lewes."
Source: BBC Sport
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