Back has signed a five-year contract, accepting a significant step down in level having resigned from Aviva Premiership outfit Leeds at the end of last season.
Rugby, who play in National League 3 Midlands, are being bankrolled by former player and businessman Michael Aland.
World Cup winner Back insists his decision to drop four rungs down the ladder of English club rugby was not based on money.
"This is an incredible challenge and one which, after a great deal of thought, I felt I could not turn down,'' said the 42-year-old Back, who was capped 66 times by England.
"I received an approach from Michael in May, less than an hour after my resignation from Leeds was announced.
"He sold me his vision of taking this famous club back to the top flight of English rugby, while doing something really meaningful for the town.
"It's a big call for me having coached in the Premiership and I have asked myself whether it's a retrograde step given how ambitious I am.
"It's not about money. Nor is this is an easy option by any stretch of the imagination, which is why I asked for a five-year contract.
"But I believe that turning around Rugby and getting the club to the Premiership would be a significant achievement and one I can use as a stepping stone to coaching at the very highest level.''
Aland plans to propel Rugby into the Premiership and hopes to build a new 30,000 capacity stadium, complete with retractable roof.
Back believes five to seven years is a realistic time frame the club to realise
their ambition of once more competing in the top flight.
"This is very much about giving the town of Rugby something of which it can be proud,'' said Aland.
"My aim is to put into place a venture which will sustain itself and be financed as a stand-alone project.''
England sevens great Ben Gollings has joined the club as player and attack coach.
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