At the age of four, Terserus lost his mother, and his father married Margareta Bure, the so-called Stormor i Dalom.

Terserus was sent to study in Västerås, where Bishop Johannes Rudbeckius took a special interest in his unusual statute and diligence, and whom he then accompanied on a visitation trip to Livland.

In 1632 he became a lecturer in Greek in Västerås and the following year, with the support of Carl Gyllenhielm, Johan Banér and Axel Oxenstierna, eh embarked on a study trip during which he visited the leading academies in Germany, France, England and the Netherlands.

He returned to Sweden in 1637 and resumed his position as a lecturer and also became the principal of an upper secondary school and notary in the chapter of the court.

But he was heavily criticized by Professor Enevald Svenonius [sv; fi], who was a defender of pure Lutheranism and accused of Terserus of syncretism.

Its decision resulted in the withdrawal of Terserus' writings; he was suspended from exercising his episcopal duties in Turku in 1664.