It begins at the New Jersey state line in the hamlet of Tappan and runs generally northward for 10.92 miles (17.57 km) to an intersection with U.S. Route 9W (US 9W) in Clarkstown.

NY 303 was assigned as part of the 1930 renumbering of state highways in New York, and only minor realignments have occurred since that time.

NY 303 begins as a four-lane route with mostly full access, and it retains this status until Valley Cottage.

While in Blauvelt, NY 303 briefly overlaps with CR 11, a mostly parallel county route that veers west to avoid the state park.

After the junction, NY 303 passes Palisades Center and intersects the New York State Thruway (I-87 and I-287) at exit 12, a modified partial cloverleaf interchange located adjacent to the mall.

The route initially followed its current alignment from the New Jersey state line north to Orangeburg, where it continued northward on Greenbush Road to its end in Central Nyack.

[7] It was redesigned in the 1990s to accommodate the addition of Palisades Center,[9][10] which was built where the formerly proposed Northern Extension of the New Jersey Turnpike would have ended at a junction with the Thruway.