The 29-year-old centre-back was an integral part of the Cod Army’s rise from the Blue Square Bet North to the Football League, captaining the side to two promotions, including last season’s title success.
McNulty arrives at Kenilworth Road on a conditional 18-month deal and goes straight into the Town squad to face his former club Barrow on Saturday.
A product of the Liverpool academy, Steve has also served Burscough and Vauxhall Motors anbefore signing for Fleetwood for £17,000 in June 2009 from Barrow.
McNulty has made 19 appearances in League Two this season, scoring twice, and featured 155 times for the club, scoring seven goals in total.
Town boss Paul Buckle said: “I think we’ve been crying out for a leader at centre half since I’ve been at the club.
“George (Pilkington) was a leader, he led by example and wasn’t necessarily the biggest talker, he’d be the first one to say that.
“Janos (Kovacs) can lead by example at times, with his height, but the other night (at Grimsby), if you’re honest, we got bullied by Cook.
“Anything that went up, we got bullied. I don’t want to see that anymore, I’m fed up with seeing that now, so McNulty will be a great acquisition.
“He’s a leader, someone who had his hands on the (League) trophy the last time I saw him. Sometimes he might not be too easy on the eye for certain people, but you have to look at his leadership qualities.
“He trained with us this morning and his voice. That’s real leadership. You can’t go on the football field as a defender and just look after yourself, you need to lead people, pull people around.
What I want to see is someone in our back four who turns around and says. ‘here is how we’re going to do it, you come here, you go there, and lets clear this ball in’, because the ball in against Grimsby just went into the goal.
“We’ve got to try and eradicate that from our game and the only way we do that is by changing personnel.
“He’s desperate to come to Luton and I want people who want to have success.”
Fleetwood Town chairman Andy Pilley paid tribute to the departing defender as he added: “First of all, I’d like to put it on record, that we wish Steve the very, very best at Luton Town. He’s been absolutely fantastic and one of the best players in my nine year era at Highbury.
“He’s been hugely influential – both on and off the pitch, played an enormous part in us winning two promotions and he’s just been superb. I think a lot of people don’t realise just how good of a footballer he really is and what a good lad he is.
“He makes the manager’s job an awful lot easier because he, too, won’t accept defeats or draws and wants to win every single game. I cannot speak highly enough about him and he’s always welcome at Highbury. I will be eternally grateful for everything he’s done for Fleetwood Town”.
For all the latest Luton Town FC news, reports, stats, player profiles, live match updates, MOM poll, prediction table and a complete fixture list, visit our Hatters Microsite.