The Brisbane Broncos have moved to beef up their inconsistent forward pack by signing Sydney Roosters prop Martin Kennedy on a three-year deal.

Kennedy, on the fringes of Queensland State of Origin selection this year, adds 122kg of muscle to the Broncos pack in a switch which comes three days before the Roosters' NRL qualifying final against Manly.

The 24-year-old has been named on a six-man interchange bench but is likely to play at Allianz Stadium with Jared Waerea-Hargreaves sidelined with suspension.

Broncos coach Anthony Griffin believes Kennedy is the ideal man to add extra starch for his side after they missed the finals for just the third time in the club's history.

"He's a big boy, he's a 120-odd kilo, and his best football is in front of him because he is only 24 years old," said Griffin.

"From a straight football point of view, it was great to get someone of his calibre into our pack. It will add to our depth there."

Kennedy enjoyed a strong start to 2013 before a knee injury prevented him from being the Maroons' 18th man in game two of State of Origin in Brisbane.

He returned from the bench in last weekend's victory over South Sydney to seal the minor premiership.

"Martin has been around - he played in the 2010 grand final - and he has been very close to Origin selection over the last year or so," Griffin said on Wednesday.

"I think he is coming here at the right time of his career because I am sure his best football is in front of him.

We are really looking forward to him coming and adding to the pack we have got."