Extra-role behavior also called organizational citizenship behavior is critical for organizational effectiveness. The purpose of this study is to develop and test an integrated model of organizational citizenship behavior based on the framework of organizational effectiveness suggested by Katz (1964) in the specific context of university teachers. The study is specifically aimed at finding the individual and joint direct and indirect effect of human resource management practices (HRP) and transformational leadership style (TSF) on affective organizational commitment (AC) and organizational citizenship behavior (OCB) of university teachers in Pakistan (developing country) and England (developed country). No other study has modeled these variables together. Data was collected through mailed and self-administered questionnaires consisting of standardized scales. Two samples of university teachers, one from Pakistan (n=402) and other from England (n=188), based on complex probability sampling were used in the study. One-way ANOVA was used to find the association of demographic factors (public and private nature of university, designation, qualification, tenure, gender, marital status and age) with affective commitment and citizenship behavior of university teachers. It was found that most of demographic characteristics caused significant variation in both affective commitment and citizenship behavior of teachers in both Pakistan and England. Correlation analysis showed significant positive associations among all four study variables. Stepwise multiple regression analysis was used to find direct effect of predictors (HRP and TSF) on mediating (AC) and dependent (OCB) variables and indirect effect of predictors on dependent variable with mediation of affective commitment both jointly and individually. It was found that HRP and TSF have significant direct effects on both AC and OCB in Pakistan and England individually as well as jointly. AC is also significantly related to OCB in both Pakistan and England but variation explained by AC in OCB in England is substantially higher than in Pakistan. AC is also found perfectly mediating the relationship between both predictors and OCB in all three cases (1. HRP-AC-OCB, 2. TSF-AC-OCB, 3. HRP,TSF-AC-OCB) in England while in Pakistan mediation of AC is just partial in all of these cases. Results have been discussed in the light of past studies and implications for managers and researchers have also been suggested.