Born in Vaudreuil-Dorion, Quebec, Hainault began his professional career with Montreal Impact in the USL First Division in 2004, and played three competitive games for the team prior to signing with small Czech side SIAD Most.

Hainault played there alongside former star striker Horst Siegl and made 46 appearances for Most in the Gambrinus liga and the Czech 2.

The Houston Dynamo announced on April 14, 2009, that they had secured Hainault's international transfer certificate from Most; he had been training with the team throughout the 2009 pre-season.

[3] Hainault turned down a call-up for two 2014 FIFA World Cup qualification matches due to an important club match-up against the Portland Timbers on October 15, 2011.

[5] After an off-season with much speculation of a transfer to Bordeaux, Hainault remained in Houston for 2012 and scored the game-winning goal over Chivas USA in the season opener on March 11, 2012.

[13] Following the season, despite reports that Ross County were set to re-sign him,[14] On July 4, 2013, it was announced that Hainault would join German club VfR Aalen of the 2.

[18] After missing significant time in the previous two years to injury, he returned to the lineup regularly and helped lead Magdeburg to promotion to the 2.

[21] On August 12, 2022, Hainault retired from active play and now serves as an Assistant Coach for the U-23 side at FSV Mainz 05.