He replaces former principal Matt Bokser, who took up the principalship at Waitaki Valley School in Kurow at the start of the third term.
Mr Hannagan, who will likely take over at Hampden for the start of term four, said he was "excited" to get his feet under the desk at the rural school.
"I'm ready for a fresh challenge. It has an interesting balance of classroom teaching and school management.
"It is an exciting, growing community and I like the feel and culture of this small rural school.
"It is part of a rural schools network with close ties to other smaller schools in the district such as Maheno and Totara."
He will commute to Hampden from the Weston home he shares with wife Julie and daughters Isla (5) and Maisie (3).
He said he had noticed differences between Weston and Hampden Schools, particularly when it came to the style employed by Mr Bokser during his time there.
"They have a practical approach to learning where they like to make it fun and hands-on. I also like the strong connections it has with the Moeraki Marae and Hampden being the tangata whenua school for the marae.
"Finally, I feel Matt (Bokser) has laid a great foundation and done many good things at Hampden that I can grow on."
Before teaching at Weston, Mr Hannagan taught at schools in Ashburton, Dunedin, Nelson and the United Arab Emirates.
