Former Porsche factory driver will rejoin the CytoSport team for the American Le Mans Series' longer races at Sebring, Laguna Seca and Road Atlanta.
CytoSport announced earlier this week that it would contest the full ALMS season with its ex-works Porsche LMP car for the first time this year, with Klaus Graf and Greg Pickett staying on as drivers.
Maassen, a former ALMS LMP2 champion, drove for CytoSport in the 2009 Petit Le Mans and will line up with Graf and Pickett again for the 2010 endurance rounds.
"He's a great team-mate, and a fantastic driver who has driven many, many miles aboard a Porsche RS Spyder," said owner/driver Pickett.
"He knows this car inside and out, and his knowledge of it is always an asset to our team."