The former Chiefs scrum-half will report for duty at Llandarcy in the summer after putting pen to paper on a contract that runs until the end of the 2017-18 season.
Capped 13 times by the All Blacks, Waikato born Leonard made 74 Super Rugby appearances for the Chiefs, scoring 16 tries, and winning the title in 2012 and 2013.
He left New Zealand after the second of those championship successes, heading into the PRO12 with Zebre for whom he has been a shining light over the last 18 months, scoring five tries in 38 games. He stole the show when the Italians grabbed a first ever win over the Ospreys in Parma last May, scoring a late touch down, while he was man of the match when they defeated Cardiff Blues at the Arms Park earlier that season.
He will link up again with his former provincial club coach, Chris Gibbes, the pair having worked together at Waikato's ITM Cup side for a number of seasons.
Speaking after finalising his impending move to the Ospreys, Leonard said:
"I'm really excited to be signing for the Ospreys. The thing that sticks out in my mind after speaking to everybody involved is that it's a club and an organisation with ambition and expectation, excellent facilities and high standards.
"Yes, I've got plenty of experience to call on, and I always want to use that to help my team mates, but I'm of the mindset that you never stop learning, wherever you are in life. What struck me the most is that the Ospreys is an environment where I'll be able to continue learning. It's something that is expected from everyone involved there.
"There's a hard working young coaching team, with strong and innovative ideas, and I'm looking forward to joining up later in the year and being a part of what they are building there. It's a good move for me professionally and personally, and hopefully, the team will continue to develop as they have this season."
According to Andrew Millward, Rugby General Manager at the Ospreys, the signing is a hugely significant one for the region.
"He's a very experienced rugby player who has played at the very highest level with the All Blacks, and has been part of a squad that won back to back Super Rugby titles" said Millward.
"That is the kind of experience that can make a huge difference within a young group of players, particularly during international periods when we lose so many leaders for some key matches. We need strength in depth if we are going to be able to compete on all fronts, right across the season, and with Brendon on board there is no doubt that we will have more strength at nine.
"His presence will help drive Rhys Webb and Martin Roberts on, as well as providing invaluable cover while Webby is away with Wales, and he can be a huge influence on Tom Habberfield's ongoing development.
"He's going to be a great addition to our squad and is an exciting signing. Anyone who has watched Brendon play will know he is a real attacking threat and will add something different to our armoury. He really understands the game and has a proper rugby brain, he's smart, and will be an asset.
"The coaches have spoken in great detail to him about the move and he's really excited about coming here. While he will play a big part on the field, what's equally important is the role he can have off the field, culturally, to help grow those around him. The hard work of the last two years to build firm foundations for the business mean that we are now in a position to secure the long-term services of key players, with Justin Tipuric signing a new deal last month, and to tactically recruit top quality players of the right calibre, such as Brendon and Paul James, who possess the characteristics that are needed for us to be successful."
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