[3] Dunham represented New Zealand at the January 2013 Australian Youth Olympic Festival in Sydney, Australia.

[1] His first international appearance at a FISA regatta was at the 2014 World Rowing U23 Championships in Varese, Italy, where he came ninth in the U23 lightweight double sculls partnered with Toby Cunliffe-Steel.

[5] At the 2015 World Rowing U23 Championships in Plovdiv, Bulgaria, he came fourth in the U23 lightweight double sculls partnered with Bryce Abernethy.

[6] Dunham went to the 2016 Summer Olympics in Rio de Janeiro, Brazil, as a reserve for the lightweight men's four but did not compete.

[8] Later that year, at the 2017 World Rowing Championships in Sarasota, Florida, the first year he competed at elite level, he won a silver medal in the lightweight single sculls; he stated afterwards that he was happy to have even made it into the A-final.