The centre has signed an 18-month deal with the Kingsholm club and will officially link up on January 1 - to the delight of head coach Dean Ryan who has swooped for the 28-year-old who can play at 12 or 13.
Ryan told http://www.gloucesterrugby.co.uk/ that he was prompted into the move because of the very real prospect of losing both James Simpson-Daniel and Mike Tindall to Six Nations duty in the new year with England.
"We have recognised the fact that both Mike and James could be called away on international duty and in that respect we need to be sure we have strength and quality in that area to go alongside the players we already have available.
"The opportunity came along for us to sign Rudi and it was simply too good to turn down. He is an exciting player, comfortable at either 12 or 13, I am sure he will be a very good acquisition for us.
"He has Super 12 experience and that is always a quality worth pursuing. It is very important we don't expose ourselves and threaten the overall strength of the squad during periods when we could lose players.
"To have Rudi on board will be a great boost for us."
Keil, who has represented South Africa Under-21s, made eight Super 12 appearances this season with one try and has represented the Sharks for four seasons and has also represented Lions in the Currie Cup.
Speaking through his agent, James Adams, Keil said: "I am looking forward to testing myself against the best in the Premiership. I am delighted to be joining Gloucester and to have the chance to experience a new challenge in my career.
"It is an exciting opportunity and I cannot wait to get started."
RUDI KEIL FACT FILE:
Club: Natal Sharks
Super 12 career: 28 appearances, 3 tries.