Britain’s Duncan Scott took gold in 1:40.54, with countryman Jack McMillan claiming silver in 1:40.94.
Sieradzki clocked 1:41.48 and shared third place with Ireland's Evan Bailey.
His medal was Poland’s fourth of the competition, following bronzes in the mixed 4x50 medley relay and the women's 4x50 freestyle relay, and a silver in the men’s 4x50 freestyle relay.
Sieradzki also swam in the men's relay alongside Piotr Ludwiczak, Ksawery Masiuk and Mateusz Chowaniec.
The 2025 European Short-Course Swimming Championships run until Sunday in Lublin, eastern Poland.
(gs)
Source: IAR, PAP