The 44-year-old, who was born in South Africa, worked with Coetzee over the past eight years at Western Province, the Stormers and Japanese club Kobe Steelers.
Proudfoot's responsibility would be scrummaging, the breakdown and all aspects related to contact areas, while another assistant, Johan van Graan, would be in charge of the attack and lineout play, Coetzee said.
“I know Matt very well from our coaching stints together in Cape Town and Japan and have a lot of respect for his ability to build a powerful pack and his rugby philosophy,” Coetzee said in a SA Rugby statement.
South Africa-born former France international Pieter de Villiers will continue to be available as scrum consultant to the team.
Proudfoot is a former Bulls front ranker who featured in the first two seasons of Super 12 rugby in 1996 and 1997. He also played four tests for Scotland between 1998 and 2003.
Coetzee was named as the Springbok's new coach last month and was given a mandate to rebuild the national side before the 2019 World Cup in Japan and to meet South Africa's rules on racial inclusion.
Coetzee has his work cut out after the retirement of stalwarts Victor Matfield, Jean de Villiers and Fourie du Preez following a bronze medal win at the last World Cup in England.
His appointment ended months of speculation over who would succeed Heyneke Meyer and his opening assignment will be three home tests against Ireland next month.
Original source: Coetzee brings in long-time ally Proudfoot