Co-hydrothermal carbonization (HTC) of lignocellulosic biomass and swine manure (SM) was conducted, and the hydrochar properties and transformation behavior of heavy metals (HMs) were investigated in this study. The results showed that co-HTC with lignocellulosic biomass promoted the dehydration of SM and enhanced the aromatization of the hydrochar. Compared to the hydrochar from SM, the carbon content, higher heating value and energy yield of the hydrochar from co-HTC were significantly increased, reaching the maximum of 57.05%, 24.20 kJ/kg and 80.17%, respectively. Significant synergy occurred between lignocellulosic biomass and SM during co-HTC and different lignocellulosic biomass exhibited similar influence on the synergy. Additionally, the concentration and bioavailability of HMs in the hydrochar from co-HTC were decreased in comparison to SM. These findings suggested that co-HTC with lignocellulosic biomass offered an effective approach to convert SM into clean solid fuel with remarkably improved fuel properties.