Saitō made his world cup debut in ski jumping in his homeland Sapporo on December 14, 1991, where he immediately came under the top 50 and thus qualified for the main competition. But he collected his first World Cup points almost 2 years later in Oberstdorf at the Four Hills Tournament in 1993. It took almost 2 years again until he was able to achieve his first top ten result. At the beginning of 1995 he reached a good 6th place on the normal hill, on the hill where he made his debut (Sapporo). This good result secured him a place at the World Championships , which he justified with a sensational 2nd place on the normal hill, only beaten by his team mate Takanobu Okabe . The Japanese were also able to "pick up" a medal in the team with 3rd place.
He celebrated his first World Cup podium with his victory on the normal hill in Chamonix at the end of 1995. Saitō was from now on a constant top 10 jumper, who won his third world championship medal in 1997 with silver in the team competition. In 1997 he was fifth in both the overall World Cup and the Four Hills Tournament . In the discipline world cup ski jumping he finished third overall. At the Four Hills Tournament in 1998 Saitō was on a podium course with second place in Obersdorf and third place in Garmisch-Partenkirchen . At the last competition in Bischofshofen he could not qualify for the second round as 35th and fell back to 13th place. His greatest success is undoubtedly his victory at the 1998 Olympic Games in front of his own audience in Nagano , where the competition was distanced by almost 40 points.
In the following years Saitō was unable to match the performance of 1996-1998. In 1999 the top 10 places were more the exception than the rule and in 2000 qualifying for the top 30 was already a problem. His last competition outside of Japan was the 2000 season finale in Planica, Slovenia . There he took 15th place in ski flying. On January 26, 2002 he started in Sapporo for the last time in a World Cup competition. Saitōs last international competition was on March 13, 2003 the Continental Cup competition in Yamagata .
In the same month he was coach of the ski team of Yukijirushi Nyūgyō and in April 2006 head coach.
Saitō can boast 16 World Cup podiums, 2 World Cup victories (in Chamonix and Willingen ), 3 world championship medals and an Olympic gold medal in his career .