Eggen was appointed as Rosenborg's coach, together with Tor Røste Fossen, and in his first season (1971) they won ""the double"" for the first time ever in the club's history. In middle of the 1970s he was the coach for the Norwegian U21 national team, and later for the senior national team. In the 1978 World Cup qualifiers, home wins over Sweden and Switzerland put Norway in contention for qualification. A loss in their final game in Switzerland meant they missed out, and it was not until 1994 that they again came close to qualification.