Immobile bagged 36 league goals in 37 outings, matching the standard Gonzalo Higuain set during the 2015-16 season with Napoli.
The Golden Shoe rewards the top scorer across every top European division, where the value of goals are weighted by the quality of league.
It's Immobile's third time capturing the accolade, putting the Italian international joint-second with eight other players on three scoring titles apiece. The decorated list includes Giuseppe Meazza, Michel Platini, and prolific former Lazio forward Giuseppe Signori.
Swedish striker Gunnar Nordahl ranks first all time after claiming five Capocannoniere titles with AC Milan from 1949 to 1955.
Immobile first won the award at Torino in 2013-14 before sharing the prize with Mauro Icardi two seasons ago. He now has 102 goals in four seasons at Lazio, most recently playing a vital role in the club's unexpected and ultimately unsuccessful Scudetto challenge.
Ronaldo, who was rested for Saturday's league finale against Roma, finished second in the Capocannoniere chase and rounded out the Golden Shoe podium positions with 31 goals this season for the Scudetto champs.