Born in 1966, Danielsen earned his grandmaster title in 1996. In 1993, he finished joint first in the Politiken Cup with Igor Khenkin and John Emms on a score of 7½/10. He has played in six Chess Olympiads: three for Denmark (1992, 1994 and 1996); three for Iceland (2006, 2008 and 2012). He is the No. 4 ranked Icelandic player as of September 2020.