O'Brien (calf) and Young (elbow) missed the recent series against Afghanistan due to injuries while Rankin was unavailable because of Warwickshire commitments.
The return of Rankin and Young will add depth to the pace-bowling department when they take on Pakistan in Dublin on August 18 and 20 but there is no place for left-arm spinner George Dockrell.
O'Brien's presence will bring experience to the top order which continues to rely heavily on Ed Joyce who scored 339 runs at 169.50 in four innings against Afghanistan. The next highest scorer was Kevin O'Brien with 145 runs in four innings.
Dockrell, meanwhile, had initially been left out of the squad to face Afghanistan before being recalled as a replacement for the injured Mark Adair. He played one match in the series taking 1 for 52. Andy McBrine and Paul Stirling will provide the spin options in this squad.
"It's great to have an almost full strength squad to choose from," John Bracewell, Ireland's head coach, said. "The bowling unit performed superbly against Afghanistan with the younger seamers in particular putting their hands up. The return of Boyd and Craig adds to that department and gives us plenty of options which is exactly what a coach wants.
"The return of Niall adds experience to the top order. We tried a few different permutations with the batting order last week - some of which worked and some which didn't. Ed Joyce was obviously the stand-out performer in his new role as opener, and it was great to see Gary Wilson return to form."
The last time Ireland faced Pakistan was at the 2015 World Cup where William Porterfield hit a century but Sarfraz Ahmed's unbeaten 101 led Pakistan to victory. In 2013, Pakistan visited for a two-match series with Ireland securing a tie in the first game of the series.
Their most famous meeting remains the 2007 World Cup clash in Jamaica which Ireland won by three wickets.