Tammelin was born in Loimaa, the son of Laurentius Petri Aboicus, vicar of Tammela, and his second wife, Brita Larsdotter.
[1] Tammelin's first published work in Finnish was Christillinen muisto-kirja, a translation of the Christliches Gedenkbüchlein by Johann Jacob Schütz.
Tammelin next translated Johann Gerhard's Meditationes sacrae (in Finnish, Pyhät tutkistelemuxet) in 1680 - this would reach 15 editions by 1909.
[2] Tammelin's father had assembled a collection of Finnish proverbs, which he called Liber Proverbiorum Fennicorum, although he did not publish it.
Gabriel Tammelin added to this collection, which was eventually published, with further additions, by Henrik Florinus as Wanhain suomalaisten tawaliset ja suloiset sananlascut (Customary and Beautiful Proverbs of the Old Finns) in 1702.