The primary responsibility of government all over the globe is to ensure security and well-being of its citizenry. In protecting her security interest in the northeastern Nigeria and Lake Chad region, Nigeria played a vital role rallying resource, political will and understand of the LCBC member statesas an aspect of its defense diplomacy to overcome Boko haram insurgency. In the Lake Chad region comprising Nigeria, Niger, Tchad, Cameroun, Boko haram activities has been responsible for over 10,000 million death and security situation in the region. This threat necessitated Nigeria defense diplomacy with LCBC to establish MNJTF. Nigeria defense diplomacy for capacity building with countries or interested partnership include joint exercises, intelligence exchange, equipment procurement and conduct of operations amongst others. The objectives of this research are to assess the influence of Nigeria defense diplomacy on capacity building of MNJTF and its impact on counterinsurgency policy, strategy and operation of MNJTF in order to defeat Boko haram insurgents in the Lake Chad. The study uses quantitative research method with an explanatory research approach. Data were collected from 97 respondents, out of a total population of 289,450 selected using a purposive sampling technique. The research result shows that: (1) Nigeria defense diplomacy has significant effect on capacity building of the MNJTF. This means that improving the defense diplomacy for capacity building have high effect in the effectiveness of the MNJTF to defeat Boko haram (2) Nigeria defense diplomacy has significant effect on the MNJTF counterinsurgency policy, strategy and operations. The research concludes that capacity building and operational effectiveness of MNJTF are influenced by Nigeria defense diplomacy with LCBC.