The probe had centred on 47 people rescued on January 19 off Libya by the Sea-Watch 3 charity ship, which was only permitted to dock on January 31 after Italy struck a deal with other European countries to take the migrants.
“It wasn't false imprisonment but simply a request for the rules to be upheld? Good!” Salvini said after the court's ruling.
“Trials and investigations do not scare me, but I am glad the judiciary confirms ports can be closed to pirate ships,” he said.
The court in Sicily ruled the Sea-Watch 3, owned by a German charity and flying a Dutch flag, had “entered Italy unilaterally and without the necessary authorisation from the coast guard”, according to Italian media reports.
The case against other senior ministers, including Prime Minister Giuseppe Conte, vice-premier Luigi Di Maio and Minister of Transport Danilo Toninelli, was also shelved.
Attempts to launch trial proceedings against Salvini for blocking migrants aboard another ship earlier this year also fell through after the Senate ruled he should not be stripped of his parliamentary protection to face charges.