Johannes Lahti finished 11th in the decathlon at both the 1976 and 1980 Olympics. He was also a top high jumper, placing second in the 1971 Finnish Championship in that event while setting a Finnish record of 2.16 metres. Lower leg problems led him to switch to multi-events. Lahti was Finnish decathlon champion in 1977-78, 1980, and 1982. His 1978 mark of 8,090 lasted as a Finnish record for 10 years. Lahti finished seventh in the decathlon at the 1978 European Championships. During his career he competed for the Turku Sports Association. He stopped competing in 1982 after a severe Achilles’ tendon injury.