The Polish cyclist defended her yellow jersey on the final stage, which finished in Alpe d'Huezin in the central French Western Alps on Sunday, securing the overall win by a narrow margin.
Dutch rider Demi Vollering won the eighth and final stage, outpacing her compatriot Pauliena Rooijakkers in a breakaway.
Niewiadoma crossed the finish line in fourth place, overtaken in the final meters by France's Evita Muzic.
Although Niewiadoma lost one minute and one second to Vollering on Sunday, she retained a slim overall lead of four seconds in the general classification.
The victory has been celebrated in Poland, with President Andrzej Duda and Prime Minister Donald Tusk among those offering their congratulations.
They hailed Niewiadoma's success as a major milestone for Polish sport.
(ał)
Source: PAP
