Nathan is likely to play in Exeter's crucial National Division One fixture against Otley at the County Ground. The Chiefs currently lead the race for promotion to the Zurich Premiership.
Nathan has missed the bulk of this season through injury, but trained with his new team-mates for the first time last week, then played his first game in two months for Exeter's United side against Henley last Saturday.
"I have been coming back from a knee injury and the club I was at don't have too many games left this season," said Nathan, who has agreed a contract until the end of the season. "Exeter are fighting for promotion and it seems like a very interesting time to be involved, so I was delighted to join.
"It's not very often that you get the chance to play for a place in the top division and that is certainly something I am looking forward to."
Already Nathan has plenty of familiar faces to help him settle into his new surroundings at the County Ground. The former Queensland Reds ace played alongside current Chief Tony Walker for Scotland A, while he also knows Gabey. He also played with Chiefs defensive coach Matt Taylor in Australia.
He added: "The quicker you can integrate into a team the better it is going to be, so it is an advantage knowing some of the guys already.
"There seems to be a really good depth to the squad and the whole club feels very professional. Training last week was very similar to what I have been used to, it was very well organised and well run."
Chiefs Director of Rugby Ian Bremner said on their official website: "With his Scotland A and European rugby experience as well as being a huge physical presence, Nathan greatly increases the options open us and is sure to have a great impact in this last and most difficult period of the season."