He married Mary Ann McDonald in 1913, and in 1914, he and his brother John Ronald Hamilton started a grain business in Winton.

His brother John Ronald Hamilton was also elected, winning the neighbouring seat of Awarua from Joseph Ward.

The Great Depression had resulted in high levels of unemployment, and Hamilton was often criticised for the government's failure to improve the situation.

He was also criticised when the Post and Telegraph Department jammed a broadcast that was expected to be pro-Labour by a private radio station by Colin Scrimgeour just before the 1935 general election.

[2] Having served as a member of the Executive Council for more than three years, Hamilton was granted the retention of the title of "Honourable" following the 1935 election.

Despite his somewhat tarnished public image, Hamilton was selected to lead the new party and took over from interim leader George Forbes.

[5] In the 1938 election, Hamilton and National were harshly critical of the Labour government and accused it of promoting communism and undermining the British Empire.

The defeat weakened Hamilton's grasp on the leadership somewhat, but any debate as to his future was cut short by the onset of World War II.

[6] Hamilton remained a part of the War Cabinet and was eventually joined by Holland despite the original claims that a National Party leader could not be in it.