The 27-year-old is quitting Roots Hall when his contract runs out and will seal his move to the Terriers once he has completed a medical.
The club expect the details to be completed in the coming weeks and boss Clark is delighted to have got his man.
"Peter is a real coup for the club," he told the Huddersfield's official website. "Just like Anthony Kay, he will join us on the back of a terrific season where he was named player of the year and although he had other options available to him, including clubs from higher divisions, we are delighted he has chosen to move to us.
"I have been more and more impressed with Peter since I have met him; he has a terrific mentality and I am sure he will become a vital member of our side.
"He is a leader, which is what I want throughout the spine of my side. We need strong, aggressive players who will not be pushed aside when it comes to the physical element of the game because then the good footballers we have will be able to get on the ball more."