The route splits from Somerset Street and heads entirely into New Brunswick, Middlesex County along French Street. At the Sandford Street intersection, Route 27 becomes a county-maintained road that is also signed as County Route 644. It then intersects County Route 693 (Jersey Avenue), which heads to the southwest to become Route 91. Past this intersection, the route becomes a two-lane street that heads into downtown New Brunswick, south of the main campus of Rutgers University. Here, the route has a daily traffic count of approximately 11,559 vehicles. It crosses under Amtrak's Northeast Corridor rail line adjacent to the New Brunswick station serving Amtrak and NJ Transit's Northeast Corridor Line. The route turns into a four-lane divided highway and intersects County Route 527 (Easton Avenue). At this point, County Route 644 ends, with Route 27 forming a brief concurrency with County Route 527, heading east along Albany Street as a city-maintained street. About later, the road crosses George Street, which heads to the north as County Route 672 and to the south as Route 171. County Route 527 splits from Albany Street by heading south on Route 171 while Route 27 continues east. After another , Route 27 intersects with County Route 514, Johnson Drive. Route 27 continues along Albany St. as a concurrency with County Route 514. It immediately interchanges with Route 18 (Memorial Parkway). At the Route 18 interchange, Route 27 becomes state-maintained again, crossing the Raritan River on the Albany Street Bridge into Highland Park.