Shinwari will play the first seven games for Melbourne before Gurney arrives to replace him.
The 24-year-old paceman from Pakistan has played 13 One-Day Internationals and nine Twenty20 Internationals for his country and recently featured in one of the T20Is against Australia.
"I have watched the Big Bash with interest in recent years and I've been impressed with the quality of the competition," Shinwari said.
"I'm hoping I can bring something different to the team with my bowling and help the Renegades push for success."
Meanwhile, 32-year-old Gurney made his international debut in 2014 and has played 12 matches for England - 10 ODIs and two T20Is. The left-armer topped 20 wickets in each of the last two domestic T20 campaigns in England and will once again share the dressing room with his Nottinghamshire Outlaws' captain Dan Christian.
"Dan spoke very positively about the competition so to get an opportunity to come and play with the Renegades is something I'm really grateful for," Gurney said. "I've had a fair bit of experience in T20 cricket in England so I'm really excited to test myself in Australian conditions.
"I have admired the BBL from afar for a few years and am thrilled to get an opportunity to play in the comp. There is plenty of talent in the Renegades squad so hopefully I can come in and play my role for the team and help us have a strong season."
Melbourne coach Andrew McDonald said the two new signings will provide some "added variation" to their bowling attack.
"We wanted to add in a left-arm seam option to provide some added variation to our attack and Harry and Usman will certainly provide that," he said.
"They'll complement our bowling unit really well and give us plenty of options throughout the innings.
"In the last few months we've been able to add in some established Big Bash players in Dan Christian and Cameron Boyce, some exciting international talent and some really promising young players. We've also been able to retain the bulk of last season's squad so competition for spots in the final XI will be fierce."
Squad: Aaron Finch (capt), Cameron Boyce, Dan Christian, Tom Cooper, Zak Evans, Marcus Harris, Mackenzie Harvey, Jon Holland, Usman Shinwari, Tim Ludeman, Joe Mennie, Mohammad Nabi, Kane Richardson, Will Sutherland, Chris Tremain, Beau Webster, Cameron White, Jack Wildermuth.
First Published: November 7, 2018, 2:03 PM IST