The hard-running prop is one of six uncapped players promoted from the England Knights to Wayne Bennett’s squad ahead of Wednesday’s Test against France.
Leeds Rhinos duo Liam Sutcliffe and Ash Handley, Hull FC full-back Jamie Shaul, Castleford Tigers second-row Oli Holmes and Widnes Vikings’ Matt Whitley are the others all hoping to make their debut in the game at Leigh Sports Village.
Leeds scrum-half Richie Myler has also been added to Bennett’s squad, not only for the game against France but also the forthcoming series versus New Zealand as a replacement for Castleford’s Luke Gale who pulled out last week due to injury.
The Knights players will rejoin that group to fly out to Australia on Thursday - Mulhern’s 24th birthday - ahead of a training camp in Brisbane and two internationals in Papua New Guinea against the Kumuls.
“If someone had told me at the start of the season I’d be training with England now I’d have laughed at them; it’s been crazy,” said Mulhern, who overcame a serious knee injury midway through the season to help Rovers avoid relegation.
“All the boys have been class with all us Knights lads.
“It’s been great just to train with them.
“I was like a sponge just trying to pick up everything off guys like James Graham and the Burgess twins, season NRL players who play in my position.
“I was listening to it all.
“We had a really good session with the Knights last week and it’s put us in good stead for this; everyone knows what’s expected of them.
“Wayne Bennett is one of the best coaches in the world. He expects big things so it’s good we’ve been prepared.”
Bennett has made the call-ups because of the involvement of nine of England’s squad in Saturday’s Betfred Super League Grand Final at Old Trafford between Wigan Warriors and Warrington Wolves.
Wigan have six players - England captain Sean O’Loughlin, John Bateman, Oliver Gildart, Joe Greenwood, Sam Tomkins and George Williams - while Warrington trio Daryl Clark, Chris Hill and Stefan Ratchford are also given time off following their Old Trafford exploits.
They will rejoin the England camp following the France Test but at least two of the six new arrivals from the Knights are expected to feature against Aurélien Cologni’s side.
Mulhern added: “I’m over the moon. When I got the phone call from JP (England football manager Jamie Peacock), if I’d not have had his number, I think someone would have been winding me up.
“To know you’re in Wayne Bennett’s thought-process is a massive confidence boost and just makes me want to kick on even more now so that hopefully in two or three years I’ll be nailed-on as a starting spot in the side.
“It’d be unreal (to play France). If I get that chance, then brilliant. It’d cap off a mad year but, if not, it’s a great experience and I can’t wait for the Knights trip.”
Meanwhile, Myler, 28, has not played for his country since 2012 but has impressed for a struggling Rhinos side in his first season there since joining from Catalans Dragons.
Revised England and England Knights squads
England: Bateman (Wigan), G Burgess (South Sydney), T Burgess (South Sydney), Clark (Warrington), Connor (Hull FC), Gildart (Wigan), Graham (St George Illawarra), Greenwood (Wigan), Hill (Warrington), Hodgson (Canberra), Johnstone (Wakefield), Lomax (St Helens), Lyne (Wakefield), McGillvary (Huddersfield), Makinson (St Helens), Milner (Castleford), Myler (Leeds), O’Loughlin (Wigan), Percival (St Helens), Ratchford (Warrington), Thompson (St Helens), Tomkins (Wigan), Whitehead (Canberra), Williams (Wigan)
England Knights: Hughes (Warrington, captain), Atkin (Hull KR), Batchelor (Wakefield), Davies (Wigan), Evalds (Salford), Fash (Hull FC), Hadley (Hull FC), Handley (Leeds), Holmes (Castleford), T King (Warrington), Leeming (Huddersfield), Lees (St Helens), Lineham (Warrington), Livett (Warrington), Mulhern (Hull KR), Oledzki (Leeds), Philbin (Warrington), Powell (Wigan), Shaul (Hull FC), Sutcliffe (Leeds), J Walker (Leeds), D Walker (Widnes), Whitley (Widnes).
England players not available for France game because of involvement in Super League Grand Final: Bateman, Gildart, Greenwood, O’Loughlin, Tomkins, Williams (all Wigan); Clark, Hill, Ratchford (all Warrington).
England Knights players called into England squad for France game: Handley (Leeds), Holmes (Castleford), Mulhern (Hull KR), Shaul (Hull FC), Sutcliffe (Leeds), Whitley (Widnes).