"Janine has been part of the NNZ High Performance Coach Pathway, is a graduate of the HPSNZ Coach Accelerator Programme and guided the New Zealand U21 team to gold at the 2013 World Youth Netball Cup," Poole said.
"She is a highly professional and qualified netball coach, and she understands what we need to address in our high performance system to ensure sustainable success with the Silver Ferns.
"This has been a thorough process, but central to our decision was selecting a coach who can build on the team's recent performances and return us to the top of international netball.
Southby, who coached the FAST5 Ferns in 2013-2014, winning the title in both years, will step down from her role as coach of the Steel and commence her role as Silver Ferns coach from December 1. She will work with Netball New Zealand to appoint support staff, including a new assistant coach.
Southby says she is looking forward to starting the next chapter in her coaching career.
"It is an honour and a privilege to be given the responsibility of leading the Silver Ferns and working with such an exciting group of athletes," Southby said.
"I am looking forward to the challenge and working with those involved to build on the solid foundations that are already in place."
Netball New Zealand will name a group of Silver Ferns triallists next week to attend a camp in Auckland from December 7-11. From this camp, the 2016 Silver Ferns Squad will be selected.