Background: The contribution of Fast-Moving Consumer Goods (FMCG) to environmental depletion is surprisingly high. Green consumption of the Fast-Moving Consumer Goods (FMCG) sector would be an effective way to reduce the global environmental footprint. Studies related to FMCG's green consumer behavior in developing countries such as Sri Lanka are few and far between. Objectives: Considering the above, researchers in the study have tried to comprehend the factors affecting green consumerism in urban Sri Lankan in the FMCG sector. Hence the objective of this study is to scientifically research the factors affecting green consumer behavior and to promote the concept in developing nations. Methods: This research has applied the Theory of Planned Behavior (TPB) & Theory of Consumption Value. Researchers have used the value and attempted to introduce another factor affecting green behavior: Green Functional value, into the study. All the above variables were measured its appropriateness in influencing FMCG green purchase Intention and Behavior. A sum of 522 usable sets of responses was extracted with the help of a scientifically prepared questionnaire using a Proportionate stratified random sampling approach. SEM (Structured Equation Modelling) was applied to measure the strength of the relationships that existed among constructs. Results: The research findings reported that TBP supported the Green consumer purchase intention, which influenced the green buying behavior Subjective norms, which is a prominent construct of the TPB, was not supported as an influence on Green FMCG Buying intention. In contrast, new extensions like Eco literacy, Green functional value, WPP were supported with a statistical significance. It was proven that the addition of new variables improved the predicting power of green purchase intention and green purchase behavior in the TPB framework. Amongst others, WPP had the highest effect on the green buying intention with very high Q2and f2 values. Related implications and a discussion are embedded at the end. Conclusions: Subjective norm's influence on green buying intention is not accepted in Sri Lankan FMCG green market. At the same time, Green trust also seems not influencing Sri Lankans' green buying intentions. The new dimension introduced, called green functional value, seems substantially influencing the green buying intention of Sri Lankan Green consumers. The willingness to pay a premium (WPP) has a very significant positive influence on Green Consumer Intention for FMCG products. The basic stem of TPB, their positive relationship between Green Purchase Intention and Green Purchase behavior, is significantly validated in this research.