In March 2012 Paltrinieri won the Italian 800-meter freestyle title, and two months later, he left everyone in his wake at the European Championships in Debrecen, defeating renowned Hungarians Gergő Kis and Gergely Gyurta in the 1500-meter.

At the end of 2012 Paltrinieri finished 2nd in the 1500-meter freestyle event at the 2012 FINA World Swimming Championships (25 m), and was later awarded a gold medal after a positive doping test for Danish swimmer Mads Glæsner.

[9] In 2014 Paltrinieri at the Italian Swimming Championships in Riccione finished second in 800-meter freestyle event with a time of 7:43.01, behind Gabriele Detti who established a new European record in the distance.

The day before the meet, Paltrinieri had swum an unofficial world best time of 50:56.50 in the 5 km (long course pool) at the Italian indoor distance championships in Riccione.

Later he won the 1500-meter, setting a new European record, a race in which Sun did not take part despite having qualified for the final with the second best time after Paltrinieri.

At the end of the year Paltrineri took part at the 2015 European Short Course Swimming Championships in Netanya (Israel); here he established a new 1500-meter freestyle world record of 14:08.06 winning the gold medal ahead fellow Italian and friend Gabriele Detti.

With the gold medal, Paltrinieri also became the simultaneous holder of the world and European titles, in long course and short course, in the 1500-meter freestyle event.

[12][13] He shared the podium with fellow Italian Gabriele Detti, who won the bronze medal with a 14:40.86 to finish less than seven seconds behind Paltrinieri.

[19][20] On the fifth day of the World Championships, Paltrinieri ranked fourth in the prelims heats of the 1500-meter freestyle, qualifying for the final with a time of 14:28.11.

[25] At the 2022 World Aquatics Championships, held in Budapest, Hungary, he ranked fourth in the 800-meter freestyle preliminaries on the third day of pool swimming competition at Danube Arena, advancing to the final with a time of 7:46.24.

[36][37][38] Two days later, he won the gold medal in the 10 km open water swim with a time of 1:50:56.8, which was less than two seconds ahead of silver medalist and fellow Italian Domenico Acerenza.

[44][45] Day two of the 2022 European Aquatics Championships, held in Rome in August, Paltrinieri ranked third in the preliminaries of the 800-meter freestyle, qualifying for the final with a time of 7:48.91.

[62] For his final event, the open water mixed team relay later in the day, he swam the third leg of the relay, challenging the third leg swimmer from Hungary, Dávid Betlehem, and contributed to a final time of 59:43.1 to win the gold medal a little over 10 seconds ahead of the team from Hungary.

[63][64] In Eilat, Israel, in November as part of the fifth and final leg of the Marathon Swim World Series for the year, Paltrinieri helped finish in a time of 1:06:37.00 in the 4×1500-meter mixed open water relay and win the bronze medal.

[65] The following day he won the 10 km open water swim with a time of 1:46:41.80, sharing the podium with Marc-Antoine Olivier of France and Dávid Betlehem, and bringing his overall World Series ranking up to first to tie Kristóf Rasovszky of Hungary for the title for the year.