Powerful front row forward Botha is known for his strong prowess at the scrum and joins the Welsh region after attracting interest from a number of leading clubs.
He will replace popular Moldovan Dmitri Arhip at the Liberty Stadium after the Ospreys confirmed he has accepted a contract offer to play in France’s TOP14 next season.
Botha is the fourth new face confirmed ahead of the 2018-19 campaign and joins Wales stars Aled Davies and Scott Williams and Namibian international Lesley Klim in committing to the Ospreys.
“I’m really excited to join the Ospreys. I enjoy the Guinness PRO14 more than Super Rugby as it’s based more on scrums, forwards mauling and stuff like that,” said Botha, 27.
“I love all the forward related stuff, that’s the strong point of my game.
“I spoke to a few of the South Africans who have played for the Ospreys before I decided to sign and they all said only good things. I can’t wait.”
Renowned in his homeland as a destructive scrummager, Botha stands 1.79m tall and weighs in at 110kg. He spent two years in France with Montpellier before returning to South Africa with Eastern Province Kings.
In 2016 he made his Super Rugby debut, playing 15 times for Southern Kings that season before signing a two-year deal with the Bloemfontein-based Cheetahs.
Last year he made 10 Super Rugby appearances before the Cheetahs switched to the PRO14.
He has played in 16 of their 19 games in the competition this season including their 44-25 defeat of the Ospreys at the Free State Stadium in September.
Dan Griffiths, Rugby General Manager at the Ospreys, welcomed the signing of Botha.
He said: “Tom is somebody that we are excited about seeing in an Ospreys shirt. He has a wealth of experience playing and scrummaging against opposition from just about every major rugby nation.
“Working alongside Allen Clarke in an Ospreys environment he has the potential to be a great asset to the club.
“He is an aggressive scrummager who likes to attack the opposition and has acquitted himself very well with the Cheetahs since his arrival in the PRO14. He is a player that thrives on the challenge that comes with the set-piece in the northern hemisphere.
“There was considerable interest in his services so we are pleased Tom has agreed to come to the Ospreys this summer and that he believes it is the right place for him.”
