Sunderland signed Jack from reigning Barclays Premier League champions Manchester City in August 2014.
A number of clubs were interested in the box-to-box midfielder, who penned a five-year deal on Wearside having joined for an undisclosed fee.
Jack rose through the ranks at Everton, making his debut at the age of 16 in a European tie against AZ Alkmaar in December 2007.
His league bow – as a substitute against Sunderland at the Stadium of Light – came three months later before the Southport-born midfielder went on to become a regular for the Toffees.
Jack, who has been capped at senior level by England, made 109 appearances for Everton before joining Manchester City in summer 2012.
He spent two seasons at the Etihad Stadium, during which time he represented City in the UEFA Champions League as well as the Barclays Premier League and domestic cup competitions.