The former St Helens chief will succeed head coach Terry Matterson from next season on a three-year deal.
Millward, 51, has seen off competition from his old adversary during Saints’ glory days – ex-Bradford Bulls coach Brian Noble – and Hull KR boss Justin Morgan to land the Wheldon Road role.
The Australian, who delivered two Super League titles and twice lifted the Challenge Cup with Saints, famously led them to become the first English club to hold three titles in one season following their 2002 World Club Challenge success over Brisbane Broncos.
However, he was just as notorious for his forthright views and outspoken manner during five years at Knowsley Road, eventually being sacked for misconduct in May 2005.
Millward took over at arch-rivals Wigan Warriors a fortnight later, but was dismissed within a year following some poor results and returned to Australia as North Queensland Cowboys assistant and, later, Canberrra Raiders’ defence coach.
He returned to England last year with Leigh – the club he started at – and led the Championship club to Northern Rail Cup success against Halifax in July.
Millward will take over a Castleford side blessed with possibly the British game’s finest clutch of youngsters, nurtured well by Matterson who is heading home to Australia after six years with the West Yorkshire club.
He took them to within a whisker of the Challenge Cup final last month, they were early-season Super League leaders, while a win over Hull FC on Saturday would confirm only their second play-off spot in nine years.
”I respect the job Terry (Matterson) has done over a long period of time; he has done fantastically well this season,” said Millward, who will move across the Pennines to live in Castleford, seeing a need to “integrate” with its fanatical supporters, and expects to make a number of signings for 2012.
“I’m looking forward to continuing the development of the team and progressing it further,” he said. “I returned to the English game via three years in the NRL and came back for family reasons.
“I’ve since been able to assess what is compatible from the NRL for Super League. I’ve also done my high performance coaching level 4 in this time.”
Castleford chief executive Richard Wright, who hopes to soon get the go-ahead for a purpose-built new stadium, has spent two months assessing candidates and spoke to senior players for input.
“Ian’s CV speaks volumes; he’s constantly monitoring new developments and techniques in both the English and Australian games, and has ideal sports science contacts which is becoming increasingly important,” he said.