The 24-year-old lock has been strongly linked with the move over the summer and Edinburgh coach Alan Solomons hinted to the media last week that an announcement was imminent.
Mata scored a try in his country’s 43-7 victory over a Team GB side that included Scots Mark Bennett and Mark Robertson, in the inaugural Olympic sevens final last month.
It was a first ever Olympic medal for the South Pacific nation and Mata said: “My goal was to win the gold medal for Fiji and we got it. Now my goal is to perform well for my new team.
“I am excited about signing for Edinburgh Rugby, and am looking forward to playing for the club.
“I am also excited about arriving in the city and meeting my new team-mates.”
After switching codes from rugby league, Mata has represented current World Rugby Sevens Series champions Fiji at nine events on the circuit, scoring 55 points through 11 tries.
The powerful middle-row, who can also play back-row, stands at 6ft 5in tall and weighs just over 18 stone.
Mata further joins new forward signings Nick Beavon, Lewis Carmichael, Kevin Bryce and Viliami Fihaki at the capital club.
Solomons, pictured inset, said: “We are delighted to welcome Bill to the club.
“He is a hugely talented player who was part of the Fiji Sevens team that recently won gold at the Rio Olympics.
“He is big, powerful and explosive and I believe he will add huge value to the team.”
Mata joins a growing band of players from or of Pacific island heritage at Edinburgh.
Samoa-born Sasa Tofilau and Solomoni ‘Junior’ Rasolea, who has Fijian heritage, formed the centre pairing in the opening Guinness Pro12 match at Cardiff Blues on Saturday, which Edinburgh lost 34-16.
Nasi Manu, Will Helu and Fihaki also add a South Seas flavour to the squad this season.
Meanwhile, Edinburgh’s next opponents, Scarlets, whom they host at BT Murrayfield on Friday night, have taken young loosehead prop Luke Garrett on loan from Newport Gwent Dragons.
Scarlets have a number of injuries at loosehead and the 21-year-old, originally from Tredegar, will remain at the Llanelli-based region until the end of the year.
Garrett, who has represented Wales U20s in the Junior World Championships in 2015, made his debut for the Men of Gwent during Judgement Day in April 2015 against Scarlets. He also played his part in the Newport Gwent Dragons’ Premiership Select side during last seasons British and Irish Cup campaign.
Dragons head coach, Kingsley Jones said: “We are happy to co-operate with the Scarlets and assist them in their current situation.
“This is a fantastic opportunity for Luke to gain experience and accelerate his development by gaining some invaluable experience in the Guinness Pro12 and potentially European competitions.”