The Pro 14 outfit have signed the 26-year-old from London Irish, whom he joined in January this year.
Prior to that, he had only ever played for the Blue Bulls in his homeland, although he came close to joining Ulster 12 months ago but failed a medical.
He will join up with his new team-mates at the beginning of next season, subject to a medical and a work permit being granted.
Head coach Johann van Graan has worked with Botha before at both club and international level for the Bulls and Springboks and says he is looking forward to linking up once again.
Van Graan said: "In building our squad for next season I believe Arno will be a great addition to our side, adding further depth and strength to our back row options.
"From my time with the Bulls and South Africa I have first-hand experience of what Arno is capable of.
"A physical ball carrier and lineout jumper, he leads by example with his work-rate, commitment and physicality, and we look forward to welcoming him to the province."