Joseph said the signing of the first five-eighth was a real confidence boost for him, his coaching team, players and the whole franchise.
Slade (22) was in the All Black training squad last year but never made it on to the paddock.
He has impressed at first five-eighth for Canterbury this year and looks the logical No 10 for the Highlanders next season.
As a first building block for the team Joseph is looking to construct for next season, Slade is a great foundation.
Over the past three years the Highlanders - since the departure of Nick Evans - have struggled to get a quality first five-eighth.
Having a competent player in that role is key for a successful campaign and Slade looks like a quality player.
He can also play at fullback but will be pencilled in by Joseph to wear the No 10 jersey.
The former Christchurch Boys' High School pupil, who has played for the New Zealand Colts and the Junior All Blacks, has been asked by the All Black selectors to play first five-eighth for Canterbury this season, despite Blues first five-eighth Stephen Brett also turning out for the red and blacks.
With the World Cup looming next year, Slade needs playing time at the pivot position to be a contender for the national side.
His path is blocked at the Crusaders by Dan Carter, so he has made the decision to move south.
Joseph, who started in the coaching role only last week, said signing Slade was great news for the Highlanders.
"He wants to come down here and show he has the ability to play for the All Blacks and play in the first five position," Joseph said.
"As a confidence boost for the coaching team, the players and the franchise, it is a great move for us. We want to provide the platform so he can play well and makes those ambitions reality."
Slade had taken his time to make the decision, as it was a big step for him, Joseph said.
Slade had been the first-choice fullback for the Crusaders in the past season but with All Black Israel Dagg moving to the Crusaders from the Highlanders, Slade's hold on the position looked shaky.
Joseph said he had been talking to other players about joining the Highlanders but they wanted to get this weekend's rugby out of the way before announcing their intentions.
Taranaki and New Zealand Maori lock Jarrad Hoeata is one earmarked to come south, while Manawatu halfback Aaron Smith and Tasman winger Kade Poki are also names that have been mentioned.
Loose forward Adam Thomson has yet to make a decision on where he will play his rugby next year, although he is being pursued by the Crusaders.
With franchise direct contracting, players no longer have to sign with the franchise encompassing their province.
Joseph is busy watching games and talking to players and agents as he assembles a team.
With the Super 15 taking in 18 games next year, an enlarged squad of 32 will be named, along with eight wider training group members.
