Several clubs monitored the midfielder’s progress, including Crystal Palace, Sunderland, Stoke City, Port Vale and Lincoln City but Pompey were determined to win the race for his signature.
After swooping for the 19-year-old, Blues boss John Mousinho said: “We do feel that he has a very promising future in the game, but we also believe that he can make an impact for us during the forthcoming season.
“Terry can run, he can compete and score goals.
“He’s an attacking midfielder who adds qualities to our group that we don’t already have.”
Former Dungannon Swifts youngster Devlin was impressed with the League One side’s determination to seal the deal.
“I’m looking forward to getting started, it will be tough but it’s also an exciting opportunity,” said the talented teenager.
“Portsmouth were the club that was most keen to sign me, they really wanted me and outlined their plans to me.
“It was a no-brainer call given the size of the club, their fanbase and their ambitions to get the club back where they belong.
“They are ambitious and so am I.
“The main aim is promotion to the Championship.
“There was interest from other clubs but Portsmouth put the foot down and when they are so keen to sign me, it is hard to turn the opportunity down.”
This may be early in Devlin’s career but he has already had to work hard and make big sacrifices.
One big call was giving up gaelic football to focus on his chosen sport.
“I have always had that ambition to be successful from a young age,” he added.
“I played gaelic as well as football and had to give the gaelic up a few years ago to pursue football. I went hard at it and it’s paid off.”
Those who have worked with Devlin believe he can become a senior international in the future.
The rising star has played for Northern Ireland Under-21s and trained with the senior men’s team. Northern Ireland boss Michael O’Neill wants young players to thrive in England and Scotland.
Strong performances in Portsmouth’s first team may convince O’Neill that Devlin can be part of the Euro 2024 qualifiers.
“International football is the next step after hopefully I can establish myself in the Portsmouth team,” continued Devlin.
“It would be nice to get a breakthrough to the senior panel.”