With pervasive international maritime security threats in the region, especially sea piracy and oil theft, Nigeria loses huge sums of money in export revenues and this reverberates on the wellbeing of residents of coastal areas whose major means of livelihood depends on the maritime sector. The purpose of this paper was to assess the impact of international maritime security threats on economic development in coastal areas of Delta and Rivers States with particular reference to unemployment and poverty levels in the areas. This paper is built around the structural conflict theory of Marxism paradigm at state-level of analysis, which is vital in the understanding of how international maritime security is related to the exploitative nature of the capitalist system, which enabled economically advanced countries to buy cheap stolen crude oil from coastal areas in Nigeria. The sample size of the study was 385 respondents drawn from a population of 9,925 people comprising of staff from Ministry of Foreign Affairs, Nigeria Customs Service, Nigeria Police Force and Nigeria Maritime Administration and Safety Agency in delta and Rivers States. The population of the study equally includes staff drawn from Togolese, Benin republic and Senegalese embassies Abuja as well as operators of shipping businesses, fishing groups and oil servicing firms in Warri, Port Harcourt, Oporoza and Bonny. Primary data were collected from close-ended and open-ended questionnaire and in-depth interview. Also, data were collected from secondary source. Data from questionnaire were analysed using simple percentages and absolute frequencies, while data from in-depth interview were analysed using narrative analytic technique. Data from secondary source were analysed using relational-content analysis. Findings showed that international maritime security threats in Nigeria maritime domain increases poverty and unemployment levels in coastal areas of Delta and Rivers States as well as transnational cooperation as well as collaboration are among the effective measures in combating negative impacts of international maritime security threats in Nigeria coastal waters on coastal areas in delta and Rivers States. Among other things, it was recommended that the federal government should urgently activate the use of relevant international instruments for combating sea piracy and oil theft in the coastal areas in Rivers and Delta States for enhanced economic development.