Olli Rahnasto was a professional tennis player in 1982. In individual he could show significant success in his career hardly why he specialized in the men's doubles. His first doubles title in 1985, he celebrated in Cleveland with Leo Palin. His next two finals he reached in 1991 in Athens and 1992 in Long Iceland. In Athens, he was defeated at the side of Menno Oosting against his compatriots Jacco Eltingh and Mark Koevermans in three sets. In Long Iceland and he Gianluca Pozzi had to the Americans Francisco Montana and Greg Van Emburgh smooth with 4:6 and 2:6 beaten. Only in 1993 could Olli Rahnasto celebrate his second title on the ATP Tour. Together with Daniel Orsanic he secured with 6:4, 1:6 and 6:3 against Juan Garat and Roberto Saad tournament victory in San Marino. In 1995, he finished his career. The highest quotation in the tennis world ranking he reached in 1989 with position 88 in the singles and in 1986 with position 79 in doubles.
In the singles at the French Open and the U.S. Open he reached the second round of the Grand Slam tournaments in 1989. In the doubles competition, he was also able to repeatedly reach the second round. In the mixed competition, he retired in Wimbledon from as early as the opening round.
Olli Rahnasto graduated from 1982-1995 a total of 24 games for the Finnish Davis Cup team. He won 17 games the majority of his 29 matches played, while he has 13 wins to have a negative balance in a double with 9.