Marine plastic litter poses several threats to its marine environment as well as to the economy. This study estimates the willingness to pay (WTP) of marine plastic litter reduction on the Sri Lankan coast by employing the One and One-Half Bound dichotomous choice contingent valuation (CV) method. CV data were collected from 600 people from the western and southern provinces of Sri Lanka, using an annual environmental tax of the next five-year period as the scenario. The truncated mean annual WTP for the reduction of marine litter was LKR 2,585 ($12.93) per household. On a national scale and with the discount rate of 15% for the five-year period, the aggregated present value was LKR 26,442.23 million ($128.37 million). Attitude survey suggested that the potential adverse impact on tourism industry is one of the key driving factors of WTP, and national policies to increase the public knowledge of marine litter would stimulate pro-environmental behaviours and improve the policy support.