Propulsion unit for an electric, pedal-assisted bicycle comprising an electric machine having a stator and a rotor, rotatable about a motor axis, said rotor being operatively connected to a crank pin, defining a crank axis, mechanically connected to pedals, and coaxial with the motor axis, wherein the rotor is coaxial and external with respect to the stator so as radially enclose the rotor. The propulsion unit comprises at least one electronic unit for operating and controlling the functioning of the electric machine, and at least a pair of housings that define a containment space which houses the electric machine and at least partially the crank pin.