A single-shaft dual expansion internal combustion engine includes an engine block, a cylinder head, a single crankshaft, a control shaft and first, second and third multi-link connecting rod assemblies. First and second power cylinders and an expander cylinder are formed in the engine block. First and second power pistons are moveable in the first and second power cylinders and are connected to respective first and second crankpins of the crankshaft. An expander piston is moveable in the expander cylinder and is connected to a third crankpin of the crankshaft. First and second multi-link connecting rod assemblies are coupled to first and second swing arms of the control shaft. A third multi-link connecting rod assembly is coupled to a third swing arm of the control shaft.