Its length is 34 km (21 mi) and it forms a single continuous route with S16, which begins at the endpoint of S51 near Olsztyn.

[1] In February 2008 the Olsztyn division of GDDKIA revealed the construction project of expressway S51.

In December 2017 the full section of expressway between Olsztynek and Olsztyn opened to traffic.

In July 2019, bypass of Olsztyn (S16/S51) was finished, making S51 complete.

The majority of Expressway S51 shadows the previous route of national road 51.