Improving smallholder farmer market participation (agricultural commercialization) has seen the advent of a number of initiatives from collective action, extension service provision and even programs that utilize ICT tools in the provision of market information. Collective action through farmer groups is an important social asset for smallholders that continue to face challenges in accessing both input and output markets. The objective of this study was to assess the effect of participation in collective action initiatives on household agricultural commercialization (market access) and household agricultural income. The study utilizes propensity score matching technique to assess the effect of collective action initiatives on household agricultural commercialization and on household agricultural income. Results indicate that farmers participate in collective action initiatives for good reasons which include enhanced access to markets and improvement of their incomes. This study brings into perspective the effects of participation in collective action initiatives both on market participation and on smallholder incomes. It finds that participation in collective action initiatives significantly increase household output and input market participation by about 9 percent and 8 per cent respectively. It also improve household welfare by increasing incomes (by about Ksh. 3400 per growing season). We discuss implications for policy and practice.