Priestland's good form for the Scarlets in the remainder of the 2010–11 season meant he returned to the Wales set-up for a match against the Barbarians in June 2011, coming on as a late substitute for Stephen Jones as Wales lost 31–28, before being included in a 39-man training squad ahead of the 2011 Rugby World Cup. In his first start for Wales, against England at Twickenham on 6 August 2011, Priestland was initially selected at full-back, but made a last-minute switch to fly-half after Stephen Jones was injured in the warm-up; Priestland kicked two conversions in a 23–19 loss. He again started at fly-half in the return match at the Millennium Stadium on 13 August, scoring two penalties before being replaced by Aled Brew at half-time; Wales won the match 19–9. Having seemingly done enough to earn a place in Warren Gatland's World Cup squad, Priestland was left out of the final warm-up match against Argentina.
Priestland returned to fitness in time to play in Wales' friendly match against Australia on 3 December 2011, starting ahead of Ospreys fly-half Dan Biggar. In addition to scoring two penalties, Priestland also crossed for his first international try as Wales lost 24–18. For the 2012 Six Nations Championship, Gatland selected Priestland and Hook as his two fly-half options, with Priestland starting all five matches, despite entering the tournament with lingering knee injuries. In the third match against England, he received the first yellow card of his international career. Full-back Leigh Halfpenny was given the goal-kicking duties during the tournament, so Priestland scored just three points: a penalty against Italy in the fourth match. Wales won all five of their matches in the 2012 Six Nations, claiming their third Grand Slam title in eight seasons.