We report on graphene-based Josephson junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to ∼ 2 K, at which point we can detect a small, but non-zero, resistance. We attribute this resistance to the phase diffusion mechanism, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further characterize the nature of electromagnetic environment and dissipation in our samples. PACS numbers: 74.45.+c, 74.50.+r, 72.80.Vp Josephson junctions with a normal metal region sandwiched between two superconductors are known as superconductor-normal-superconductor (SNS) structures. Over the years, the normal region has been made from non-metallic nanostructures, including heterostructures, nanotubes, quantum wires, quantum dots [1], and, most recently, graphene [2][3][4][5]. Usually, these superconductor-graphene-superconductor (SGS) junctions employ aluminum as the superconducting metal, separated from graphene by another metal layer (often titanium) intended to create a good contact. In this paper, we succeed in making palladium-lead (Pd/Pb) contacts to graphene. Here, Pd is known to form low-resistance contacts to graphene [6,7], while Pb has the advantage of a relatively large critical temperature (7.2 K). As a result, the SGS junctions demonstrate an enhanced zerobias conductance up to temperatures of the order of 5 K, and at temperatures below ∼ 2 K a clearly visible supercurrent branch appears in the I − V curves.In all of our samples, a small, but non-zero voltage is observed below the switching current. We attribute this feature to the phase diffusion mechanism [8]. The phase diffusion in underdamped junctions is enabled by the junction's environment, which provides dissipation at high frequencies [9]. Observation of this regime in our SGS junctions is facilitated by the high critical temperature of Pb. We first study the phase diffusion resistance as a function of temperature, which allows us to extract the activation energy associated with the phase slips. Next, the phase diffusion is measured at different gate voltages, resulting in a consistent picture of the junction's environment and dissipation at high frequencies. This series of measurements allows us both to establish the phase diffusion regime in underdamped SGS junctions, and to analyze their behavior in terms of well-established models. Finally, we demonstrate an efficient way of controlling the junction by passing a current through one of the electrodes within the same structure: the locally created magnetic field modulates the critical current. Several periods of oscillations are visible, indicating the spatial uniformity of the junction.Graphene was prepared by a version of the conventional exfoliation recipe [10] from natural graphite stamped on RCA-cleaned Si/SiO 2 substrates. The samples were verified by Raman spectroscopy to be single atomic layer thick with low defect...