At the 2004 Summer Paralympics in the SH2 Standing Air event, Johnson shot a perfect 600 out of 600 points in the preliminaries and then equalled the world record for a gold medal in the finals with 704.3.

Johnson later became the first New Zealand world champion, when in July 2006 he won the gold medal in the SH2 Prone Air event at the IPC World Championships in Switzerland, shooting 600 out of 600 points In 2007, Johnson attended the Jikji Cup in South Korea, competing in and winning four events: the SH2 Standing, Prone, Falling Targets and 50m Small-bore.

Johnson secured a bronze medal in the Mixed R4-10 m air rifle standing SH2 with a score of 701.2 after a shoot-off with South Korean shooter Ho-Gyoung You.

[2][3] 2009 started well with Johnson building towards London 2012 competing again at the Jikji Cup (now called The Open Asian Shooting Championships) in South Korea.

[4] At the 2010 world championships in Zagreb, Croatia, Johnson won the bronze medal in the air rifle standing event after shooting a perfect 600 / 600 points.