The seats will be available on services from Poland, Slovakia, Hungary and Romania throughout March.
In a statement issued on Tuesday (1 March), the airline said it was "committed" to helping Ukrainian refugees reach their destination, "wherever that may be".
The carrier will also offer a €29.99 rescue fare on all other flights (excluding the UAE, Iceland and the Canaries), as well as a €69.99 rescue fare on all flights to the UAE, Iceland and the Canaries, to support refugees who may be stranded in other locations.
Passengers will be required to provide their Ukrainian passport/ID card number at time of booking and show their Ukrainian passport/ID card at time of check-in.
Jozsef Varadi, chief executive of Wizz Air, said the company’s "hearts are with the Ukrainian people during this crisis".
"We are committed to helping as many Ukrainian refugees as possible to get to a safe place, which is why we will be offering them 100,000 free seats from the border countries and special rescue fares on all other flights," he added.
"We have already seen great humanitarian efforts on the ground by our people across the network, and as a company we wanted to play our part in these efforts. We would be happy to provide a safe and welcoming journey for these refugees."
The move comes following Russia’s invasion of Ukraine, which led to transport secretary Grant Shapps banning all Russian aircraft from operating to and from the UK.
In response, the Russian government barred UK-based carriers from landing in the country or entering its airspace. The EU has since imposed a blanket ban on all Russian aircraft using its airspace.
