Exiles sign SA lock
Capped by the Springboks at Under-20 level, the 25-year-old has played 43 times for the Tigers since joining them from then French Top 14 outfit Mont de Marsan in 2013.
The towering lock brings specialist skills to the line-out as well as a hard edge in attack and defence.
Born in Johannesburg, De Chaves featured prominently for the Junior Boks in their World Championship campaign of 2010 where they defeated England in the third-place playoff.
De Chaves cut his teeth in professional rugby in his native South Africa with the Golden Lions where he reached an U19 Currie Cup Final as well as playing in the Vodacom Rugby competition prior to his move to France.
"I'm delighted to be joining London Irish, a club that is steeped in tradition and has ambitions to succeed at the highest level," said De Chaves.
"There will be a lot of competition for places in the second-row, and I'm looking forward to the challenge that lies ahead," he added.
London Irish Head of Rugby Operations Glenn Delaney said: "We are delighted to have acquired a player of Sebastian's calibre and we look forward to welcoming him to the club.
"He will be a real asset to our forward pack as we continue to strengthen our squad for next season."
