We study the problem of representational transfer in RL, where an agent first pretrains offline in a number of source tasks to discover a shared representation, which is subsequently used to learn a good policy online in a target task. We propose a new notion of task relatedness between source and target tasks and develop a novel approach for representational transfer under this assumption. Concretely, we show that given generative access to a set of source tasks, we can discover a representation, using which subsequent linear RL techniques quickly converge to a near-optimal policy, with only online access to the target task. The sample complexity is close to knowing the ground truth features in the target task and comparable to prior representation learning results in the source tasks. We complement our positive results with lower bounds without generative access and validate our findings with empirical evaluation on rich observation MDPs that requires deep exploration.