Poidevin made his Test debut for the Wallabies on 24 March 1980 in a match against Fiji, which Australia won 22-9. He played over 59 caps for the Wallabies, becoming the first Australian to play 50 Tests. He captained the team on four occasions. His final appearance with the Wallabies was against England in the Grand Final of the 1991 Rugby World Cup at Twickenham, won by Australia 12-6.
After retiring from the Wallabies in 1991, Poidevin became a stockbroker, although he maintained his links to rugby by working as a television commentator for the Seven Network and Network Ten. He was Managing Director of Equity Sales at Citigroup in Australia. Simon joined Pegana Capital in March 2009 as Executive Director.