Though NC 51 begins at the state line, SC 51 is a short 1-mile-long (1.6 km) road that connects with US 21, near Fort Mill, South Carolina.

Crossing the state line, NC 51 quickly becomes a four-lane road as it goes through the town of Pineville.

In Matthews, NC 51 bypasses the main downtown area, followed by a semi-controlled interchanged with US 74 (Independence Boulevard).

[5] In 1968, NC 51 was extended to the South Carolina state line, replacing a segment of US 21.

[6] In 1981, NC 51 was placed on new alignment in Pineville, abandoning an old routing along Lee Street and eliminating a short concurrency with US 521.