The route heads through suburban areas between Newark and New Castle as a multilane road, passing through Ogletown and Christiana.

What is now DE 273 was originally built as a state highway in the 1920s and 1930s, with the portion east of Hares Corner becoming a part of US 40, which had crossed the Delaware River on a ferry between New Castle and Pennsville, New Jersey.

From the state line, the route heads southeast on two-lane undivided Nottingham Road, running through wooded suburban neighborhoods as it enters Newark, crossing the Christina River and passing to the south of the Newark Country Club.

The road crosses CSX's Philadelphia Subdivision railroad line at-grade and comes to an intersection with New London Road, which runs northwest as northbound DE 896, and South Main Street, which heads southwest as DE 896.

The route turns southeast and reaches an interchange with DE 4 and Salem Church Road in the community of Ogletown.

Past this interchange, DE 273 becomes Christiana Road and heads east through suburban residential neighborhoods with some businesses.

The road enters the city of New Castle and heads east between business parks and warehouses to the south and farm fields to the north.

[4] The section of DE 273 between Chapman Road and Browns Lane in Christiana is part of the Washington–Rochambeau Revolutionary Route, a National Historic Trail.

[10] The following year, US 40 was designated to run on the portion of road between Hares Corner and New Castle, where it connected to a ferry across the Delaware River to Pennsville, New Jersey.

Also by this time, all of present-day DE 273 was upgraded to a state highway except the portion of US 40 between Hares Corner and the Basin Road intersection in New Castle.

[14][2] The same year, a bridge was constructed over a Pennsylvania Railroad line (now the Jack A. Markell Trail) in New Castle.

[14] DE 273 was designated to run from the Maryland border west of Newark east to US 13 and US 40 in Hares Corner by 1936, roughly following its current alignment.

[17] DE 273 was realigned to bypass Christiana a year later, having previously followed Main Street through the community.