The explosion at the main mosque in the provincial capital of Puli Alam killed Governor Arsallah Jamal and wounded 15 other people, five of them critically.
Mr Jamal, 47, was a close confidant of President Hamid Karzai and served as his campaign manager during the 2009 presidential elections. He also served as governor of eastern Khost province until he was appointed to his current post in Logar in April.
A high-profile target, he had survived a number of assassination attempts in the past, including suicide bombings.
No-one immediately claimed responsibility for the attack but the Taliban have been targeting Afghan officials, military and Nato troops as part of their campaign to retake territory as international troops draw down ahead of a full withdrawal at the end of 2014.
The explosion happened as Mr Jamal was speaking inside the mosque to worshippers gathered for one of Islam's holiest days. The bomb was apparently planted inside the microphone in the front part of the mosque, officials said.
Mr Jamal was recently in the spotlight following his revelation that a senior commander of the Pakistani Taliban was taken into custody by American forces in Logar province on October 5.
US officials confirmed that Latif Mehsud, a leader of the Tehrik-e-Taliban Pakistan, or TTP, was captured by American forces in a military operation.
At the time, Mr Jamal said Mehsud was captured as he was driving along a main road in Mohammad Agha district.