It travels from the hamlet of Meldrum Bay, near the western end of the island, to Highway 6 in the community of Little Current.

The highway turns east onto Agnes Street and gradually curves southeast.

In front of the United Hall Church, the road curves south and becomes Gore Street.

The section within the town limits of Gore Bay is maintained under a Connecting Link agreement.

Its western terminus is Highway 540, and before its eastern terminus is at Highway 6, near Tehkummah, it passes through the small villages of Advance, Long Bay, Britainville, Spring Bay, Dryden's Corner, Monument Corner, Central Manitoulin, Mindemoya, Gibraltar, and Sandfield.

From Dryden's Corner, Highway 551 extends southerly a further 6.4 kilometres (4.0 mi) to its terminus at Government Road the shore of Lake Huron just outside the community of Providence Bay.