[1] Nykvist did his military service at Berga Naval Base south of Stockholm in 1987 and began his career on the submarine HSwMS Sjöhästen in 1988.

Nykvist attended the staff course at the Swedish National Defence College from 2001 to 2002 and served as an executive officer on a Gotland-class submarine from 2002 to 2004.

[5] Nykvist was stationed at the Naval Base Point Loma from 2005 to 2007 when the submarine HSwMS Gotland was leased by the United States Navy.

[4] Back in Sweden, Nykvist attended the command course at the Swedish National Defence College in Stockholm from 2007 to 2009 and then served as chief of staff of the 1st Submarine Flotilla from 2009 to 2010.

[8] He also attended the Salve Regina University in Newport, Rhode Island, USA between 2013 and 2014, receiving an MA in international relations.

[9] Nykvist was then the EU Naval Force Chief of Staff during Operation Atalanta in the Gulf of Aden from April until September 2015[7][10] and back in Sweden he continued being the commander of the 1st Submarine Flotilla until 2016.