The body of Marvin Dean Jansen, 60, of Tahuya was found by a passer-by Saturday morning at about 7:30 a.m. on the shoulder of Highway 300, also known as North Shore Road, near Belfair.
The State Patrol launched an investigation and determined that the victim was likely struck between 1 and 2 a.m. Saturday and his body had been lying on the side of the road for hours before it was spotted.
The investigation also led the State Patrol to a suspect and a pickup believed to be the one that struck the victim.
The suspect, later identified as Brandon Allen McMahon, 21, of Tahuya was questioned and admitted that hit "something" with his 2001 Dodge Ram pickup overnight and then drove away, said Trooper Russ Winger of the State Patrol.
The suspect was then arrested and booked into the Mason County Jail for investigation of felony hit-and-run.
Anyone with information is asked to call the State Patrol at (360) 473-0300.