Schmitz began his career with
TSG Sprockhövel. In July 2007, he signed for
VfL Bochum II. He made his professional debut on 18 September 2009 in a match against
VfL Wolfsburg. Schmitz used to play as a
left midfielder or a defensive midfielder. In the 2010–11 season, he became the Schalke's main left fullback. Schmitz signed a four-year contract with
Werder Bremen on 17 June 2011. In 2014, he joined
Fortuna Düsseldorf. Later on, Schmitz went to Austria to play for
Wolfsberger AC in 2018. In May 2020, he signed for
VVV-Venlo to play there until June 2022, starting from 2020–21. ==Personal life==