The Dungannon and Ulster flanker traveled to France for the 2007 World Cup but was an unused replacement throughout the tournament as Ireland crashed out at the group stages.
He had to wait until June 2008 to win just his fifth international cap but he has since gone on to become a Test regular under new Ireland coach Declan Kidney.
Now, just weeks after playing a key role in his country's first Grand Slam triumph since 1948, Ferris has earned his spot among the Home Unions' elite.
"It's a bit crazy to be honest," said Ferris, who joins 13 other Irishmen in Ian McGeechan's 37-man squad for the three-match series against the Springboks.
"It hasn't really sunk in. I don't think it will for a few weeks. I was part of a Grand Slam winning side and now I am going on a Lions tour. It is simply unreal in many respects.
"I never dreamed that I would have been winning a Grand Slam with Ireland let alone be going on a tour with the Lions a few years ago when I was starting off my professional career with Ulster.
"I am 23 years old and I am at the pinnacle of rugby. It hardly gets better than that."
One way things could get even better for the Ulsterman is if he breaks into the Lions Test team in South Africa.
Like every other member of McGeechan's touring party, Ferris knows that being named in the original squad is the easy part; making the Test XV is now the ultimate objective.
"It is one thing to have been selected for the Lions, but now I have to go there and earn my place in the team that plays," added Ferris.
"It would be great to be on the Test team against South Africa. They're the world champions.
"They're very aggressive guys but I'm just relishing the opportunity of getting out there and testing myself against supposedly the best pack in the world.
"I'm going to relish the opportunity to get stuck into them and just give it 100%, like I always do.
"If I'm in the Test side, I'll try and cause a bit of havoc. To get the opportunity to get into a Test side is massive and I'll be doing everything I can to do that.
"It's a massive challenge for the Lions but it's just great to be a part of it. It's pretty hard to believe but I'll go out to South Africa and enjoy every minute of it. It's going to be a great experience."
Among his Irish colleagues hoping to make the Lions Test team is former Ulster team-mate Tommy Bowe, a man Ferris rates highly as a player and even higher as a friend.
"It is great to have Tommy in there as well. We are the best of mates even with him being away from here now, but we keep in touch and it is just great to have him in there. I'm sure it will be a great tour."