Nicknamed "Daddy Frans", Steyn started his professional career with the Sharks at the age of 19 and made his Super 14 debut in 2007, before moving to France and joining Top 14 club Racing Métro 92 in 2009.

The player made his return for the Sharks in the 2013 Super Rugby competition, captaining the side in the first few matches in the absence of regular skipper, Keegan Daniel.

[1] On 24 March 2023, he came off sustaining a knee injury in a Currie Cup Premier Division fixture against the Blue Bulls and was ruled out for the rest of the competition that his team won two months later.

[9] After playing only ten matches for the Sharks in the 2006 Currie Cup Premier Division (at fly-half), Steyn was, at 19 years old, selected to represent South Africa in the Northern Hemisphere touring squad by national coach Jake White.

Steyn kicked two drop goals in the 2007 Tri Nations opener against Australia at Newlands Stadium in Cape Town, to win the game for the Springboks.

Steyn replaced him, playing only his second [citation needed] game at professional level at inside centre, but he made a break on first touch of the ball and his inclusion sparked the Springboks to a 37–0 second half demolition of Samoa.

He was subsequently cleared of the charge, due to insufficient evidence and Vaka conceding that the apparent "bite mark" could have been received during normal play.

Steyn was the starting inside centre for the Springboks in the 2007 Rugby World Cup Final, he made a fantastic break that resulted in a penalty for the Boks and also converted one himself later on in the game.

Steyn was re-called for South Africa for the 2017 series against France due to the injuries of Pat Lambie and Handre Pollard, after a 3-year absence from international rugby.