Within a few years, he, together with his brother Henry, took over responsibility for the farm after their parent's marriage broke down and his father moved to Australia.
[1] By 1936, Gallagher was married; he had met his wife, Millicent May née Murray, through involvement with a church at Te Puke.
Shortly afterwards, he, his other brother Vivian, and a friend began working in Wellington, making electric fences and gas producers for use with vehicles.
[1] As the Second World War was well underway, he was co-opted to work for the Colonial Ammunition Company, which had been relocated from Auckland to a site in Hamilton East.
[1] After the war, Gallagher resumed manufacturing gas producers, setting up a facility at his property on Seddon Road in Hamilton and employing six workers.
His business also carried out tractor conversions and made farming equipment, including his battery-powered electric fence.
The former played a major role in exporting the firm's products to Australia which in turn inspired Gallagher to look to develop markets in the United Kingdom.