Maramureș County
Tătaru joined the PSD in 1997. He was vice president of its Maramureș County youth organization from 1998 to 2000, and belonged to the party's national council from 2000 to 2008. From 2000 to 2004, he was vice president of the Baia Mare PSD chapter, and became first vice president in 2011, rising to president in 2016. He has also been vice president of the Maramureș County chapter since 2001. In 2008, he was elected to the Maramureș County Council, serving until 2011.