He is best known along with Jeon Myeong-un for his role in the 1908 assassination of Durham Stevens, a former American diplomat, employee of the Japanese colonial office in Korea, and pro-Japan lobbyist.

In March 1908, infuriated by Stevens' remarks about Japanese rule in Korea, the Daedong Bogukhoe held a joint meeting with the Dongnip Hyeophoe, another local association of Koreans of which Jeon was a member.

Jang then accidentally fired into the melee, striking Stevens twice in the back; Jeon was also shot in the confusion.

The crowd which had gathered urged that they be lynched on the spot; Jang was arrested and held without bail on a charge of murder, while Jeon was sent to the hospital for treatment.

[3] Jang was repatriated to Korea in 1927, where he attended the wedding of Cho Man-sik and established an orphanage in Sonchon, North Pyongan.

[4] Jang was posthumously awarded the Order of Merit for National Foundation by South Korea's Ministry of Patriots' and Veterans' Affairs in 1962.

In 1975, South Korean president Park Chung Hee ordered that he be reburied in the Seoul National Cemetery.