He is one of only two persons ever in football, alongside Didier Deschamps, to achieve 100 national matches for his country both as player as well as coach.

[7] In 1970,[6] at 20 years of age, he was brought to B 1901 in the top-flight Danish 1st Division championship by coach Kurt "Nikkelaj" Nielsen.

[9] In Olsen's first year with the club, Cercle Brugge finished in eleventh place in the 1972–73 Belgian First Division and went on to establish itself in the mid-table.

In 1980, Olsen moved to 16-time Belgian champions Anderlecht,[6] to play alongside Danish internationals Benny Nielsen and Kenneth Brylle.

[13] During most of 1982, Olsen suffered from a severe shin injury, which prompted Anderlecht manager Tomislav Ivic to move him back from the midfield into the libero position.

Olsen scored a goal in the first leg, but missed his shot in the deciding penalty shoot-out which Tottenham won.

Olsen played 80 games and scored two goals for Köln in the Bundesliga,[19] before retiring from his active career in June 1989, 39 years of age.

[20] He helped Denmark qualify for the 1972 Summer Olympics, but could not participate at the tournament, as he had signed a professional contract with Cercle Brugge beforehand.

[23] Olsen, alongside defender Søren Busk,[24] persuaded Piontek to implement the aggressive off-side trap they practiced at Anderlecht.

[25] Olsen captained the Danish team that qualified for the 1984 European Championship; Denmark's first international tournament participation since the 1972 Olympics.

Olsen was identified as one of the overall top performers at the World Cup,[26] and he was subsequently named 1986 Danish Player of the Year.

[28] Morten Olsen ended his international career following the 1988 European Championship, having played 99 national team games, but was called up again 10 months later.

Though initially filling the role of playmaker rather than a ball-winning tackler,[32] Olsen eventually excelled as a defensive midfielder possessing great determination, dedicated professionalism, and organisational skills.

[31] At the age of 32,[14] Olsen was moved back to the libero position, which transformed him from an established player to an international star-player.

[33] Olsen employed a wide variety of skills for a defensive player, including attacking surges and technical dribbling, taking advantage of his acceleration and vision of the game.

[14] He provided long passes from his deep position, while his forward surges helped create numerical advantages in the midfield.

With the notable exception of Nigerian international defender Uche Okechukwu, his dabblings in the transfer market were not equally successful.

At the start of the 1995–96 season, Köln were eliminated in the DFB-Pokal by an amateur team from Beckum,[41] and Olsen was fired in August 1995.

Olsen failed to qualify Denmark for the 2006 FIFA World Cup, but prolonged his contract with DBU in November 2005.

[47] A part of the new deal, which ran until and including the 2010 FIFA World Cup, was the added responsibility of defining a "red thread", or common denominator, in the talent work of the Danish national youth teams, thus giving Olsen a large influence on the future football being played by Denmark.

[53] However, his contract was mutually terminated immediately after the Danish national team failed to qualify for Euro 2016, beaten by Sweden 4–3 on aggregate on 17 November 2015.