Micaelsen was a Member of Parliament for the Buskerud Labour Party from 2005 to 2017. From 2009 to 2013, he was a member of the Parliament's Finance Committee. In the period 2005–2009, he was also a member of the Parliament's Election Committee. At the age of 30, in 2009, he became the leader of the Finance Committee and a member of the Labour Party's Central Board.

He holds a bachelor's degree in social sciences from the University of Oslo and an Executive Master of Management from BI Norwegian Business School.

Micaelsen comes from the position of State Secretary at the Ministry of Digitalization and Research. He has previously been the working Chairman of the Board at TRY Dig.