He was born in Holmestrand as the son of Nils Ihlen and Barbara Wincentz Thurmann. In November 1852 Wincentz married Birgitte Elisabeth Møresearch, granddaughter of Constitutional founding father Ole Clausen Møresearch, and the couple had one daughter and three sons.
During the 1860s Ihlen started as an entrepreneur and bought several local enterprises and real estate. This included the farms at Haneborg, Granholt and Vittenberg, and the Nordby saw mill. Based at Fjellhamar Farm in Lørenskog, he built up a major complex of saw mills and grain mills, establishing the first industrial complex in Lørenskog.
The background for the establishment was the new railway line that ran past Lørenskog, giving easy access to lumber from the inner parts of the country, as well as to the port in Oslo.
The mills were owned proprietorially until they incorporated as the limited company A/South Fjeldhammer Brug in 1893, and the company has today become part of Icopal. Wincentz Thurmann Ihlen established his own mechanical workshop and iron works at Strømmen in 1873, under the name West. Ihlen, Strømmen.
The main product was railway cars, with the first being produced in 1874. He died in 1892 in Kristiania.
