St. Mary's Church, Longnewton is a Church of England church in the parish of Longnewton, Stockton-on-Tees, Teesside, England. It is part of the benefice of All Saints' Church, Preston-on-Tees.
It is a small stone building in the Early English style, twice rebuilt, in 1806 and in 1858, and occupying the site of a more ancient church.
There is a nave, chancel, and south aisle; north of the chancel, forming a transept, is the Londonderry mausoleum, within which is a sculptured white marble tomb of the third Marquis of Londonderry. The present building is Grade II* listed.
There was formerly a chantry in this church, dedicated to the Blessed Virgin Mary.
The church has links with St. Mary's Church of England Aided Primary School in Longnewton.