He became the first overseas driver to win the East African Safari Rally in 1972, partnered by Gunnar Palm and again in a Ford Escort.

In 1979 he made a serious challenge at the World Rally Championship title, ultimately finishing runner-up, only one point behind champion Björn Waldegård.

Mikkola was joined by Swedish co-driver Arne Hertz in 1977 and the pair were very quickly a force to be reckoned with, winning the British Rally Championship in 1978 in an Escort.

He won the 1000 Lakes and RAC rallies the following year, but did not improve on third position in the championship, ultimately finishing behind Opel's Walter Röhrl and teammate Michèle Mouton.

He remained with Mazda until entering semi-retirement in 1991, although he continued to make sporadic appearances on international rallies until retiring completely from motorsport in 1993.