Disclosed are a polyester binder resin for coating which is copolymerized with lactic acid or a compound derived therefrom and isosorbide, and thus has a high content of biomass-derived compounds, and exhibits superior coating hardness, contamination resistance, hydrolytic resistance, processability and the like, and a coating composition comprising the same. The polyester resin binder for coating is copolymerized with a diacid component, a diol component comprising 1 to 60 moles of isosorbide, with respect to a total diol component, and 1 to 50% by weight of lactic acid or a compound derived therefrom, with respect to the total amount of resin polymerization reactants, wherein the polyester resin binder for coating has a structure in which a diacid moiety derived from the diacid component, a diol moiety derived from the diol component, and a hydroxyl monoacid moiety derived from the lactic acid or a compound derived therefrom are repeated.