Bernt Johan Collet is the son of Chamberlain and Master of the Royal Hunt Harald Collet (MSc Economics) and Else, born Collett, landscape architect. He married Catharina Marie (MA), born Löwegren, on 31 December 1968.

Bernt Johan Collet completed a degree in business economics in 1968 and trained as a production manager at Næsgaard Agricultural College after which he worked in American business for several years. Over the years Bernt Johan Collet has held a large number of directorships and honorary positions, including the chairmanship of Civiløkonomerne (former association of Danish business graduates) and the presidency of Det Internationale Økonomforbund (international association of business economists).

In 1981 Collet was elected to the Danish parliament, Folketinget, on behalf of the Conservative People’s Party, and held several official positions before being appointed minister of defence in 1987 and later Danish delegate to the UN general assembly in 1989. Collet co-authored Kilder til Danmarks Historie 1945-82 (1984) and 13 værdier bag den danske velfærdsstat (2007).