The system will be a constellation of roughly 290 satellites in low and medium Earth orbit, designed to give governments and militaries secure, jam-proof communications.
Interior Minister Marcin Kierwiński signed the deal at a ceremony in Warsaw on Tuesday alongside EU Defence and Space Commissioner Andrius Kubilius.
"This will be a completely independent system that will guarantee us security and full autonomy," Kierwiński said.
He added that Poland would be "one of six main players" in building the IRIS² constellation in Europe, and "one of the foundations" of the secure communications network for the whole continent.
He pointed to Russia's war in Ukraine, natural disasters and hybrid threats as reasons the EU needs its own resilient system, warning that communications networks can themselves be targeted.
Poland's contribution will account for about 10 percent of the constellation's value, with the country's stake worth nearly EUR 600 million, funded through the EU's recovery plan.
Kubilius called it a big day for Poland, NATO's eastern flank and the European Union as a whole.
"By investing in space, Poland is investing in its security, its economy and its future," he said, adding that the deal would make the country "a driving force" on the eastern flank.
IRIS² will eventually provide secure links for EU governments and institutions, plus broadband for businesses and residents, including in areas with poor connectivity.
First services are expected in 2029.
Starlink, run by Elon Musk's SpaceX, has become central to Ukraine's war effort, but the businessman has faced criticism for restricting Kyiv's access to it at key moments.
More recently, Ukrainian officials have accused Russian forces of using Starlink terminals to help guide attack drones.
(ał)
Source: PAP, IAR
Click on the audio player above for a report by Piotr Urbaniak.