Kaj Christiansen scored six goals in five matches for the Denmark national football team between 1943 and 1948.

[1] Christiansen moved to BK Frem, where he made his senior debut against Kjøbenhavns Boldklub (KB) on 21 March 1943.

Rather than Jørgensen's physical style, Kaj Christiansen was a quick player of great anticipation.

He scored two goals on headers in the debut game, a 3–2 win against the Sweden men's national football team, with Danish King Christian X in attendance.

Kaj Christiansen moved on to Division 2 team Grenoble Foot 38, for whom he played his last season as an active player.

He returned to Denmark, and coached Randers Freja for some years, culminating in winning the 1967 Danish Cup tournament.