The 25-year-old scored 41 goals in 165 appearances for the Seasiders following his transfer from St Johnstone in the summer of 2004.
The Terriers now boast an impressive array of striking options - with Andy Booth, Phil Jevons, Danny Cadamarteri and Luke Beckett already at the club.
"Talks about the move have been going on for a while, but we're delighted to have secured Keigan," Ternent said.
"He gives us another option up front and he's genuinely quick. He's proven at this level of football and he gives us more competition for places in attack.
"We're really pleased to have him here, but there are more to come."