 Wennström became an elite hurdler at a young age, challenging Sweden's established top hurdler Sten Pettersson and winning his first national title in 1927 as an 18-year-old.He represented Sweden at the 1928 Summer Olympics in Amsterdam and nearly qualified for the final, placing third in his semi-final.Wennström reached his peak in 1929, consistently running under 15 seconds and winning another Swedish national title; finally on 25 August, in a dual meet against Norway at Stockholm, he broke the world record with his time of 14.4.