Shoard (22) was a member of the championship-winning New South Wales Swifts last year and, despite her youth, brings considerable skill to the shooting ranks.
The Steel's initial application to include Shoard in the team was denied by Netball New Zealand.
However, the national body's attitude changed after Steel shooter Donna Wilkins gave birth to her first child, son Cooper, by Caesarean section in Invercargill on November 30.
"The basis of our application was we were concerned Donna would not feel ready to take the court on April 1 and it was approved based on that change of circumstances," Steel chief executive Julie Paterson said.
"It's a relief to now have our squad finalised. While planning continued regardless, its great to have our 12 players confirmed and we can continue moving forward with even greater momentum."
Paterson was excited to include an Australian player in the line-up.
The Steel had shooter Megan Dehn in its squad earlier this year.
"Leah will add a different perspective. She will bring in new experiences and new ideas and I think that will benefit the team as a whole."
Steel coach Robyn Broughton said Shoard's coaches across the Tasman spoke highly of the former Australia Under-21 player.
"She comes with a lot of good vibes," Broughton said.
Shoard has had a meteoric rise, making her debut for the Swifts in the Commonwealth Bank Trophy (the precursor to the ANZ Championship) in 2006 and earning an Australian Institute of Sport scholarship last year.
She was also presented with the Commonwealth Bank Trophy players' player award in 2007.
She was eagerly anticipating the move to Invercargill in January.
"I've heard it's very cold there but also very beautiful. I'm excited," Shoard said.
Despite the Swifts beating the Steel in their opening game this year, Shoard rated the Southerners highly.
"We were lucky to play them in the opening game because the Steel really started to perform well as the season progressed. I think we played them at the right time," she said.
"I've heard the Steel has a very good line-up next year with eight present or former Silver Ferns so it will be awesome to play and train alongside players of that calibre."
The Southern Steel squad is: Daneka Wipiiti, Donna Wilkins, Julianna Naoupu, Leah Shoard, Adine Wilson, Liana Barrett-Chase, Wendy Telfer, Sheryl Scanlan, Erika Burgess, Katrina Grant, Megan Hutton, Te Huinga Reo Selby-Rickit.
