In 1952, a handful of years after arriving in Australia from Ireland, Mr McCahill left for New Zealand with another native of County Donegal, Hugh Green.
In Wellington, they won a tender to lay cables for the Post and Telegraph Department, followed by another to lay 33km of cable around Auckland City.
The fledgling Green & McCahill (Contractors) Ltd bought a digger and expanded into tunnelling, sewerage and stormwater contracts and grew to become a major operator in infrastructure projects throughout the country.
Its two founders joined their workers with picks and shovels labouring day and night to complete their first contract.
"They always used to promise the guys that they'd give them more if they could do more footage than them, back in those days. Apparently no one ever won that," recalled John Green, son of Hugh Green, who died last year. Green & McCahill built roads, tunnels and dams, as well as major works at the Marsden Pt refinery and the Glenbrook steel mill.
The success of the Auckland-based company, which was divided in 2003, put both its founders on the rich list.
Mr Green said that despite that wealth, Mr McCahill, who was his godfather, retained traits gained through a rural Irish upbringing.
"He wasn't an outspoken sort of guy, he was just one of the boys. That was one of the endearing things about him. Anyone could talk to him," Mr Green said. "You would go over to his farm one day, and he'd be over there chopping up firewood and selling it on the back of a trailer for $25 a trailerload. He was a character."
Mr McCahill was a long-time member of Marist Brothers Old Boys Rugby Club. Five sons played for the club, including Bernie, a 10-test All Black. Son Sean went on to represent Ireland.
Board member Mark Sumich said Mr McCahill's help was instrumental in the shift to Liston Park in Ellerslie in the late 1960s and early 1970s.
The McCahills maintain strong links with Ireland, where two of their children live.
Irish rover
Barney McCahill died, aged 84, last Friday.
*He is survived by wife Patsy, nine children, including former All Black, Bernie, and former Football Fern, Terry, and five grandchildren.
*In 1952 left Australia for New Zealand.
*Mr McCahill was a long-time member of Auckland Marist Brothers Old Boys Rugby Club. Five sons played for the club, including Bernie, a 10-test All Black. Son Sean went on to represent Ireland at international level.