Duffy, 37, has joined the third-placed Championship side on a one-year contract after leaving Swinton Lions.
The Scotland assistant coach will lead Featherstone in their final league game against Toulouse on Saturday before the upcoming Super 8 Qualifiers.
"He is a fantastic coach and we are very excited to see how his reign here unfolds," chairman Mark Campbell said.
"We believe he has done a remarkable job in extremely difficult circumstances at Swinton and he deserves a great deal of credit for his efforts there."
Duffy, who played for Leigh, Widnes and Salford during a 16-year playing career, has been replaced by his former assistant Stuart Littler at fellow Championship side Swinton.

Greater Manchester Police (GMP) apologised for racial stereotyping for using a fake terrorist shouting "Allahu Akbar" in the mock terror attack.
Organisers of the meeting at Longsight Saath Saath are demanding an inquiry.
GMP said it has no plans to issue any further statements on the training exercise staged at the Trafford Centre.
The scenario for the mock suicide bombing was by an extremist Daesh-style organisation although GMP had said the event was not linked to any specific terror threat.
Syed Azhar Shah, who chaired the meeting attended by about 30 people, said GMP assistant chief constable Garry Shewan's apology was not enough and "only acceptable" if those responsible resigned.
He said while the training exercise was a good idea but it was "shocking to portray Muslims as terrorists" and that only one group would commit terrorist acts.
He said: "It is also shocking what our children and community who live in this country will see themselves as; terrorists or British citizens?"
Mr Shah said further events would be held to "condemn this" and "ensure this would not happen again".
He said one apology "would not mend so many hurts".
One of those at the meeting said using a Muslim as a terrorist sent out "the totally wrong message" and "puts a wedge" between the community and GMP.
"We are all British citizens. As far as Islam is concerned it does not permit any killing."
Greater Manchester's police and crime commissioner Tony Lloyd, said it was "frustrating" the operation had been "marred by the ill-judged... and unacceptable decision" to have the terrorist shout 'Allahu Akbar' before setting off fake bombs.
Other locations in the three-day counter-terrorism exercise include Redbank Community Home in Newton-le-Willows.

The 70-year-old Time Team presenter joined anti-tunnel campaigners to fight the plans, saying they placed the area's wider archaeology at risk.
The protest by the Stonehenge Alliance was staged outside a consultation event in London earlier.
Highways England said it was working to find "the best solution possible".
The public consultation on its plans for putting the A303 into a 1.8-mile (2.9km) dual carriageway tunnel runs until 5 March.
Highways England says the move would cut congestion and improve journey times.
The scheme has the backing of English Heritage and the National Trust.
Speaking outside the Society of Antiquaries at Burlington House, Robinson suggested a longer tunnel.
He said: "I think the proposal we are being offered is a really old-fashioned one.
"It assumes what needs to be protected is that little clump of stones."
He said it was only over the past three decades archaeologists had begun to comprehend the wider significance of the site.
"That's a high-class Wiltshire Disneyland experience," he said.
"Once it's gone, we'll never get that back.
"If you were going to protect Buckingham Palace, you wouldn't put a tunnel in halfway down the Mall."
The Stonehenge Alliance wants other options to reduce traffic to be fully explored.
Spokeswoman Dr Kate Fielden said: "We want a genuine consultation with real choice.
"Both of Highways England's options involve huge and damaging new roadworks gouged into our most important ancient landscape."
A spokesman for Highways England said: "We fully understand the cultural heritage of the site and one of the broad objectives of the scheme is to help conserve and enhance the World Heritage Site by removing the sight and sound of traffic and make it easier to reach and explore."
Featherstone Rovers have appointed John Duffy as head coach following the departure of Jon Sharp.
[NEXT_CONCEPT]
Police have been accused of "institutional racism" for portraying a suicide bomber as an Islamist terrorist, a protest meeting heard.
[NEXT_CONCEPT]
Actor and broadcaster Sir Tony Robinson has said plans for a tunnel near Stonehenge in Wiltshire are too "old-fashioned" in outlook.