August Petri was a student of the Italian Fencing Master Arturo Gazzera who started teaching in Offenbach in 1899. Petri was one of 11 fencers belonging to five fencing clubs who founded the Deutschen Fechter-Bund (DFeB) in 1911. He helped write its charter and served as its first secretary. In 1921 Petri was on the FC Offenbach team that won the épée team event at the German national championships. In 1926 he became president of the DFeB but had to resign in 1928 for personal reasons.
Petri competed in two Olympic Games in 1906 and 1908, fencing with all three weapons, foil, épée and sabre. In 1906 in Athina he won the gold medal with the German sabre team, the first time Germany won an international title in fencing. He also came in fifth in team épée and in the individual épée, and was eliminated early in individual foil and the two individual sabre events. Two years later in London he competed in the individual sabre and épée with limited results, and claimed fifth places with both teams.