Southby played for the Western Flyers in the National Bank Cup competition from 1997 to 2001, before transferring to the Dunedin-based Otago Rebels in 2002.
In 2006 Southby was announced the new coach of the Rebels franchise, and held that position until the National Bank Cup made way for the new ANZ Championship in 2008.
She was unsuccessful, with Sting coach Robyn Broughton winning the position and opting to select former Silver Fern Donna Wilkins as her assistant.
[3] After a franchise review by Steel chief executive David Bannister in late 2012, Southby was promoted to head coach for the 2013 season.
In July 20, 2018, silver ferns coach Janine Southby had resigned in the wake of Netball New Zealand's independent review of the team's disastrous Commonwealth Games campaign, in which they did not even collect a medal.