Tuilagi is the latest summer signing by Bedford, who finished fourth in the second tier of English rugby last season.
“We wanted to add a bit of firepower to the back row and Fred looks like he fits that bill in terms of that ball-carrying ability,” said director of rugby Mike Rayer.
“He’s been out of the English scene for a few years but wants to establish himself back in the game and see how he can kick his career on.”
Bedford have a home pre-season game against Blackheath on Friday before taking on Saracens and Northampton, Premiership champions for the past two seasons, on 6 and 13 September.
Their opening match of the new league season is at home to Caldy on 21 September.