During the Romano-British period, the Romans built a roadside settlement on the site of a Corieltauvi settlement. It was traditionally thought to have been named Causennis, although that is now believed to be Saltersford near Grantham. Ancaster lies on Ermine Street, the major Roman road heading north from London. To the northwest of Ancaster is a Roman marching camp and some 4th-century Roman earthworks are still visible. Excavations have found a cemetery containing more than 250 Roman burials, including 11 stone sarcophagi. In the later years of Roman occupation, a large stone wall with accompanying ditches was erected around the town, possibly for defence against marauding Saxons.
The place-name 'Ancaster' is first attested in a twelfth-century Danelaw charter from the reign of Henry II, and in a legal document of 1196, where it appears as Anecastre. The name means 'the Roman fort of Anna'.
An excavation by television programme Time Team in 2002 revealed a cist burial bearing an inscription to the god Viridius. The dig also uncovered Iron Age to 3rd-century pottery, a 1st-century brooch, and some of the Roman town wall.
In 2005 the once widespread but now rare Tall Thrift plant was discovered in Ancaster churchyard, one of only two locations within the country where the plant is found. A preservation regime for the plant was instituted by English Nature.
The town Ancaster located in Ontario, Canada was first established in Upper Canada in 1792 and was named after Ancaster, Lincolnshire by British army officer and the first Lieutenant Governor of Upper Canada Governor John Simcoe who was apparently inspired in the name choice by Peregrine Bertie, the 3rd Duke of Ancaster and Kesteven.