The Tamar Valley Line is a railway line from Plymouth, Devon, to Gunnislake, Cornwall, in England, also known as the Gunnislake branch line. The line follows the River Tamar for much of its route. Like all railway lines in Devon and Cornwall, it is unelectrified and all trains are diesel powered. The entire line is single track past St. Budeaux Junction.

Gunnislake is a large village in east Cornwall, England, United Kingdom. It is situated in the Tamar Valley approximately ten miles (16 km) north of Plymouth The first woman cabinet minister in the British Empire, Mary Ellen Smith, was born here in 1863.