Blackadder had announced that this season would be his eighth and final year in charge at the Crusaders, who were top of the Super Rugby standings heading into the international break as they chase a first title since 2008.Robertson has spent the last three years as coach of the Canterbury provincial team and led New Zealand to the World under-20 title in 2015.
"We had a highly contested process with some exceptional candidates, so that made it a very difficult decision in some ways," Crusaders chief Hamish Riach said in a news release.
"However, we are very excited about what Scott Robertson offers this team and thrilled to be appointing him to the role."
Robertson, who played 23 tests for New Zealand between 1998 and 2002 and 86 times for the Crusaders, has been handed a three-year deal to take him through to the end of the 2019 season.
"This is a team I have played for, am passionate about and looking forward to leading," he said.
"The head coach of the Crusaders is regarded as one of the best jobs in the world, so I couldn’t be more excited to be taking it on.
"When I think about the remarkable men who have done the job before me ... I am humbled and honoured to be stepping into their shoes.
"The previous and current coaching teams have built an impressive legacy and I take the responsibility of continuing and building on that legacy very seriously."
The Christchurch-based Crusaders are by far the most successful team in the two-decade history of the Super Rugby competition, having won the title in 1998, 1999, 2000, 2002, 2005, 2006 and 2008.
(Reporting by Nick Mulvenney, editing by Ian Ransom)
