Among low income workers, labor supply is often irregular: frequent shocks disrupt work spells, absenteeism is high, and many workers prefer flexible casual work to formal jobs. We examine the possibility that labor supply is habit forming—so that past labor supply levels affect preferences for future supply. We undertake a field experiment with casual urban laborers in Chennai, India. We randomly provide some workers with small financial incentives for attendance over 7 weeks, leading to a 23% increase in labor supply. We test for habit formation by examining subsequent impacts after the incentives are removed. First, we see a persistent 16% increase in labor supply over the next 2 months, resulting in a 11% increase in employment. Second, treated workers exhibit a higher willingness to accept work contracts that are of longer duration and less flexible. They also self-report an increase in automaticity—suggesting a change in preferences. Third, shocks that temporarily pull workers out of the labor market lead subsequent treatment effects to collapse to zero; in the absence of these shocks, we cannot reject that there is no decay in effects over time. Fourth, in incentivized measures, employers accurately predict treatment effects, and prefer hiring workers who have been treated with a stronger habit stock in the past—findings that have relevance for understanding duration dependence and the “unemployment scar”. Finally, in supplementary data from other settings, we replicate short-run persistent effects of transitory labor supply shocks—indicating the broader generalizability of hysteresis in labor supply. Together, our results suggest that the intermittent nature of employment and frequent shocks experienced in low-income settings may inhibit workers from becoming habituated to regular work—with implications for the transition to formal regular work in poor countries.