In the following season, Griffin continued to be a regular part of the first team, making 16 appearances in the 2012–13 league, starting all but one of these games. Connacht featured in the top European competition again that season, with Griffin playing four times in the 2012–13 Heineken Cup. In the 2013–14 season, he played 19 times in the league and four times in the Heineken Cup. Following rumours that would join Munster, it was announced in February 2014 that Griffin had signed for English Premiership side London Irish and would leave at the end of the season. He made a total of 71 appearances in his first spell with Connacht.