The Official Online RBS 6 Nations Store is open. The store has everything you need to get behind your team during the RBS 6 Nations, plus the store is now fully stocked with a much wider range of rugby merchandise.
Confirmation of his move to Stradey Park comes just two days after the Scarlets sacked their rugby director Phil Davies.
Davies, along with Scarlets chief executive Stuart Gallacher, recently returned from a scouting mission to Australia and New Zealand.
New Zealand prop Greg Somerville is another Llanelli target who could agree terms in the near future.
Gallacher said: "I met with David and his representatives in Sydney last week in what was an extremely productive meeting.
"David outlined his reasons on why he wanted to play in Europe. And with a change of lifestyle and new surroundings, we are confident he will flourish with the Scarlets."
Lyons, 27, broke his ankle playing for Australia against Canada in the World Cup last autumn, but is now back to full fitness.
And his arrival in Llanelli means the Scarlets' Wales back-row forward Alix Popham has been freed to join England World Cup winners Ben Cohen and Steve Thompson at French club Brive.
Llanelli have secured a six-figure compensation fee from Brive for an early termination of 33 times-capped Popham's Llanelli contract.
Popham said: "I've had a great three years at Stradey Park and really enjoyed my playing career with the Scarlets.
"But this is a great opportunity for me and my family to experience a new culture and lifestyle."