The 24-year-old, named by police as Michał O., died at about 04:30 a.m. local time on Monday.
He had been in a critical condition since being taken to hospital with gunshot wounds, and underwent at least three operations, regional governor Krzysztof Jan Klęczar said.
On Saturday, the man drove a car onto Kraków’s Main Square and opened fire with an automatic weapon "on random people," according to officials.
Six people were killed and 16 injured, including two police officers.
Eryk Stasielak of Poland’s National Prosecutor’s Office said the gunman’s death would not halt the investigation.
Prosecutors will continue to examine his motives and any possible links, he added.
"We are at an early stage," Stasielak told reporters, adding that there was a great deal of evidence to analyse and that all identified witnesses would be questioned.
The inquiry also covers the killing of three of the gunman’s close relatives, whose bodies police found at the family’s flat in Ostrowiec Świętokrzyski.
Investigators believe he killed them too, and the probe covers both cases.
Fifteen people injured in the attack remain in six hospitals in Kraków, the governor said.
Fourteen are in a stable condition, while one – a police officer – is seriously injured.
Post-mortem examinations on the victims in Kraków and Ostrowiec Świętokrzyski are due to begin on Monday.
Prosecutors say they could take two days because of the complex nature of the gunshot wounds.
(ał)
Source: PAP