In February 1957, aged 18 and working as a bank clerk, he won his first talent quest as an out and out rock'n'roll performer and finally agreed to sing at Auckland's Jive Centre. No-one was prepared for what was to follow. By the time he completed his set, girls were screaming and everyone else was awestruck with what they'd heard.
A hurried recording of Lawdy Miss Clawdy - another Presley song - followed and launched Devlin as New Zealand's first superstar when it was released in June 1958.
Initially radio stations ignored it but teenagers were buying it and once sales topped the 2000 mark, the radio stations could no longer turn a blind eye to this boy from the River City. Within a few weeks it was at the top of the Lever Hit Parade.
Come November 1958 and Devlin had released three singles which sold 50,000 copies. Between November 1958 and May 1959, a further eight singles were released along with three EPs and an album, amassing total sales in excess of 200,000.
A nationwide tour followed with chaos breaking out at every performance. The country had seen nothing like it. He was constantly making headlines and mobbed by screaming girls. A South Island was bedlam.
After celebrating his 21st birthday in Whanganui, Johnny moved to Australia and while he was moderately successful there his reign as a social phenomenon was over. It had lasted a mere 12 months.
Johnny continued to record while in Australia and between 1959 and 1981 he released a further 40 singles, 10 EPs and three albums. He also wrote The Games Are On, the official song for the 1974 Commonwealth Games in Christchurch.
He continued performing on the club circuit in Australia but in June 2015 the 77-year-old Devlin suffered a heart attack while on board a P&O cruise ship.
He was transferred to St Vincent's Hospital, Sydney in critical condition and received a triple bypass which saved his life.
In 2007 he was inducted into the NZ Music Hall of Fame and the following year was appointed a member of the New Zealand Order of Merit for services to entertainment in the New Years honours.
In 2009 Johnny was presented with New Zealand's "Biggest One Hit Wonder of the Century Award'', just edging out Ray Columbus with his She's a Mod.
The Variety Artists Club of New Zealand presented him with the Benny Award in 2015, the highest honour available for a Kiwi variety entertainer.