Number eight Lyons won 44 Australia caps between 2000 and 2008
David Lyons has completed his move to Stade Francais, a day after the former Australia international was released early from his Scarlets contract.
The number eight, who had one season remaining on a four-year Scarlets deal, was allowed to leave to secure a long-term deal in France's Top 14.
The 30-year-old, who joined from the Waratahs in July 2008, follows
Regan King out of Parc y Scarlets
"I had always planned to play in France," said Lyons.
"And I've been working closely with the region for some months now on my release.
"I'm looking forward to the opportunities ahead of me now and the chance to pursue my ambitions with a French club."
Lyons played only 16 times in the Scarlets' 32 competitive fixtures last season and coach Nigel Davies sanctioned the Aussie's early release because of the emergence of number eight Ben Morgan.
The 22-year-old, who won three man-of-the-match awards in his 15 starts last season, was
one of 21 players who signed contract extensions
tipped Morgan to be a Wales star of the future
and the young back-rower will have more chances to push his international claims - Morgan is dual-qualified for Wales and England - now Lyons has left the Scarlets.
“This Scarlets team will only go from strength-to-strength with the core of players they have gaining in experience”
The Scarlets' back-row strength - they also have Welsh internationals Josh Turnbull and Rob McCusker - gives coach Davies enough reassurance to allow Lyons to leave.
And Lyons admitted: "There's some really good young players coming through for the region and I'm pleased to have played my part in helping bring some of them through.
"You've got the quality and ambition of some good young blokes in the back row, they will put their body on the line and won't shirk anything.
"It's a really good young side and the guys play an exciting, attacking brand of rugby which has been great to be part of."
Lyons follows former New Zealand scrum-half Byron Kelleher and Argentina fly-half Felipe Contepomi to Paris as one of 20 summer signings for Stade Francais.
Davies praised Lyons's impact in Wales, saying: "David has played an important role within our group over the past three years and he leaves knowing that he has made a significant impact on the squad of younger players we have coming through.
"He has always been a consummate rugby professional, his experience and approach with younger players has been valuable to us at key times within our season and he did a sound job last year leading the Scarlets as captain when Mark Jones was injured."