He was born in Trondhjem a son of estate owner Albert Collett and Nanna Høegh.
In 1912, he married Baroness Ingeborg Wedel-Jarlsberg, daughter of estate owner Baron Carl Gustav Wedel-Jarlsberg of Atlungstad and Amalie Thomine Michelet.
Arthur Collett graduated as a medical doctor at the Royal Frederick University in 1905 and was conferred the dr.med.
Early in his career, he was district physician in Modum and deputy consultant in pediatrics at the National Hospital 1911–1915.
He published several scientific works on pediatric topics, such as infant mortality, child care and infant care, including as an expert for the League of Nations.