Manager Joe Kinnear, who has been chasing Hartson for some time, admitted: "I'm delighted. John is a smashing lad and a top-quality striker who has proved himself with 24 goals last season.
"He's only 23 but he is experienced and skilful.
"People might wonder at the size of the fee for a club like Wimbledon but I have half a dozen worth that much in my squad."
Hartson, who will sign a six-year deal if he passes a medical, said: "This is a great move for me.
"Joe has worked wonders and I know Wimbledon style needs someone like me - a strong target man who can score goals."