Lars Tammelin (2 May 1669 – 2 July 1733) also known as Laurentius Gabrielis Tammelinus was a Finnish mathematician and prelate who was the Bishop of Turku from 1728 to 1733.
Tammelin was born on 2 May 1669 in Turku in the Swedish Empire, the son of Gabriel Larsson Tammelinus and Anna Eriksdotter Pihl.
In 1698 he became a professor of mathematics at the Royal Academy of Turku.
In August of the following year, he undertook a study trip through Denmark, Germany and the Netherlands where he enrolled at Leiden University on 27 November 1698.
He studied under the Cartesian mathematician and astronomer Burchard de Volder, and returned to Finland in the autumn term of 1699.