Collett was born at the family manor house Rønnebæksholm (Rønnebæksholm Gods) in Næstved, Denmark. He was the son of Johan Collett (1734-1806) and Maureen Elisabeth Jensen (1746-1788). He was educated at the University of Copenhagen and graduated in 1791. Educated in the law, he soon entered public service. In 1795, he was appointed Bailiff in Numedal and later Kongsberg year. He replaced Herman Wedel Jarlsberg as acting County Governor of Buskerud in 1813 and was succeeded by his brother Johan Collett in 1814.  
Collett was a Member of Norwegian Parliament in 1814, 1818, 1824 and 1827. He played an important role in the events of Norway in 1814 and became known as one of the "Eidsvoll men". Together with Niels Aall, he led the negotiations with Swedish general Magnus Björnstjerna which resulted in the Convention of Moss. Later, he participated in several government positions. He was a prominent minister and received the post of First minister when the former First minister Mathias Sommerhielm left Christiania in 1822. His position made him the most prominent minister, although with political power than that of the Governor of Norway. When governor Baltzar von Platen died in 1829, no new governor was appointed, and Collett subsequently became the highest authority in Norway until he left office in 1836, except for a brief period in 1833 when Crown Prince Oscar was appointed viceroy. 
He was married in 1797 to Maren Christine Collett (1777-1860), daughter of landowner Peter Collett (1740-1786) and his second wife Johanne Henriche Ancher (1750-1812). He died in Christiania (now Oslo) and was buried at Vår Frelsers gravlund.
- Tor Ragnar Weidling. "Jonas Collett". Store norske leksikon. Retrieved June 10, 2016.
- "Rønnebæksholm Gods". VisitDenmark. Retrieved June 10, 2016.
- Terje Bratberg. "Collett". Store norske leksikon. Retrieved June 10, 2016.
- "Johan Collett (1775-1827)". eidsvoll 1814. Retrieved June 10, 2016.
- Odd Arvid Storsveen. "Jonas Collett – 1, Statsråd". Norsk biografisk leksikon. Retrieved June 10, 2016.
- "Jonas Collett". Regjeringen. Retrieved June 10, 2016.
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