"I'm pleased to have agreed a new contract. Andy and I have a long-term vision for the club and we know it will be challenging," said former Heineken Cup winner Back.
"This year we want to build on the achievements of last season and then we believe the club can really begin to flourish."
The Amlin Challenge Cup side finished runners up in pool one last season on their return to European action and face a stern test this time around with former Heineken Cup finalists Stade Francais Paris alongside them in Pool 4.
"This is an exciting time to be involved with Leeds Carnegie and Yorkshire rugby in general. The potential at Leeds Carnegie is huge and I am very much looking forward to seeing that process through in the coming years," added Key.
Leeds travel to Romania to face Bucharest Oaks in their first pool game before hosting Stade Francais Paris at Headingley Stadium.
Italian side Crociati Rugby round up Leeds' European opponents, with the two sides set to meet in back-to-back encounters in December.