Stradey Park product Peel has been at the west Wales club for 10 years and will leave at the end of this season.
He said: "My move's not about money as the deal to stay at Llanelli was similar to that offered by Sale - it's about the fact that, not having lived outside Wales, I'd like to experience life in another country for a short period."
Llanelli Scarlets chief executive Stuart Gallacher said: "Dwayne has served us admirably through one of the club's most thrilling decades.
"He has been a cornerstone in helping us to develop a formidable European record in that time and in keeping us highly competitive in domestic tournaments.
"We're always pleased to see home-grown talent become international stars - and Dwayne has served Wales and the Lions with great skill and dedication.
"His departure leaves a void at Stradey Park but means that the tremendous emerging talent in Phil Davies's squad will be given a greater chance to shine. We will also be looking to strengthen the squad."
Llanelli Scarlets director of rugby Phil Davies said: "We wish Dwayne well at Sale - he has served our region extraordinarily well and is hugely popular with fans and teammates.
"He has been outstanding for us in the Magners League and Heineken Cup and will be a credit to his new club. Having never been based outside Wales, this will be an exciting adventure for him. I believe he would like to return to Wales and we'd be delighted to talk to him in the future about him coming home to the Llanelli Scarlets."
Peel's honours include Wales schools, Wales under 16, 19 and 21 caps.
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