Marianini started his career at Lucchese. In summer 2003, he joined Triestina of Serie B in co-ownership deal, but bought back in June 2004 and sold to Serie A side Lecce. After Lecce relegated, he joined Empoli of Serie A and followed the team relegated to Serie B in 2008.
In June 2010, he left for Serie B newcomer Novara on a three-year contract. On 18 July 2012 he added one more year (to 2014) to his current contract.