Stuart-Smith made six appearances for the league leaders last season, including a starting role at Headingley in the Tykes' final home game of the season.
Commenting on his signing, Director of Rugby Phil Davies said, 'Clive is an extremely talented young player who has all the ability to develop into an international class scrum half. He has shown at Gloucester this season that he can handle playing in the Zurich Premiership and hopefully he will develop even further at Leeds.'
The Tykes have also confirmed that scrum half Derek Hegarty and winger Chris Hall will not be retained for next season. Hegarty made 20 appearances in all competitions last season after joining Leeds from Munster, whilst Hall ends a three-year spell at Headingley having scored 29 tries in 60 games, including 17 in the promotion winning season from National Division One after joining from Morley.
Davies added, 'Derek has always given 100 per cent during his time at Leeds and has been a tremendous person to have involved with the squad, both on and off the field. He stated that he would like to return home to Ireland to continue his playing and I was glad that we could come to an agreement.
'Chris has spent three seasons with us and I would like to thank him for his efforts whilst at the Tykes and wish him all the best for the future,' added Davies.
The Tykes are hoping to confirm details of their pre-season campaign by the end of this week as they prepare for the club's first ever season in the Heineken Cup.