The deal, which reportedly includes a $16 million signing bonus, comes two months after the Lions signed Backus to a one-year, $6.93 million contract that included a promissory note: that they wouldn't give him a franchise tag designation in 2007.
The new contract makes Backus the sixth highest paid offensive lineman in the league and the highest paid lineman that has never been to selected to a Pro Bowl.
Backus is expected to be a large part of offensive coordinator Mike Martz's pass happy offense, which demands near perfection from the left tackle, blind side position. A six-year veteran, Backus has not missed a game since joining the team as a first round draft choice.
He adds stability to one end of a unit that is expected to improve drastically under offensive line coach Larry Beightol.