Beds Police Chief Constable Alf Hitchcock is leaving the force after two and a half years.
Mr Hitchcock, who joined Beds Police in October 2010, has been appointed next Chief Constable of the Ministry of Defence Police.
Central Beds councillor Richard Stay said on Twitter: “Sad day for Bedfordshire, Alf Hitchcock has done a good job.”
The force is also currently recruiting for an Assistant Chief Constable.
Mr Hitchcock said: “I am incredibly proud of what officers and staff have achieved since I arrived in Bedfordshire in January 2011.
“The force has undergone significant change and overcome many challenges over the last two years, but as a result Bedfordshire is a county where crime is reducing, detections are increasing, and public satisfaction in what we do is rising.
“I know that the fantastic colleagues I am leaving will continue to fight crime and protect the public with the commitment and enthusiasm that I have been so proud to have been a part of.”
Police and Crime Commissioner Olly Martins said: “I would like to express my gratitude to Alf for the strong and effective leadership that he has provided to Bedfordshire Police over the past two years, and I wish him well with the new challenge he faces at the MoD Police.
“I am sure that in doing so I also speak for the force, the public, and for the partner agencies that work alongside the police.
“Alf leaves a Force that is both cutting crime and delivering rising levels of victim satisfaction with the service they receive from the police.
“So my job now is to secure the best Chief Constable for Bedfordshire that I can, who will build on the firm foundations that have been laid by Alf, and with whom I look forward to forging a similarly close working relationship.
“Since my arrival at Police HQ I have been impressed by the strength and quality of leadership across Bedfordshire Police.
“This is why I am confident that the Force will deliver its side of the bargain in terms of my plan for an ever stronger partnership between local people and their police.
“This in turn is how we will deliver the long-term sustainable reduction in crime we all want to see”.
A Beds Police spokesman said Mr Hitchcock was currently away on holiday and his leaving date had not yet been confirmed.