 He won the triple jump title at the national athletics championships in 1934 and 1935, and was second in the same event but the leading New Zealander (behind Japanese athlete Kenshi Togami) in 1937.Brainsby served with the 21st Rifle Battalion, 2nd New Zealand Expeditionary Force during World War II.He rose from the rank of sergeant to become a major on General Freyberg's staff, and returned to New Zealand after the battle of El Alamein.