Polish government spokesman Adam Szłapka said the deal would deepen the two countries' existing Nato alliance commitments, providing a framework for joint military exercises, intelligence sharing and closer security cooperation.
Cybersecurity and health security are among the areas specifically covered.
Speaking on Tuesday, Tusk said Poland had sought provisions aimed at "genuinely increasing Poland's security in peacetime, so as to prevent potential threats".
He noted that both countries are already working closely together on support for Ukraine, which he described as a further reason to intensify security ties.
The treaty builds on defence cooperation agreements the two countries signed in 2017 and 2023.
It is expected to include a mutual defence commitment, along lines similar to deals the UK has recently concluded with France and Germany.
Beyond defence, the pact covers economic resilience, energy security, illegal migration and crime.
For Starmer's Labour government, the agreement is part of a broader effort to rebuild relations with European partners following years of post-Brexit tension.
The British prime minister has recently said he wants to put his country to be at "the heart of Europe".
Tusk drew a parallel with a similar treaty Poland signed with France in Nancy a year ago, which included a mutual military assistance clause and cooperation on defence industry, the economy, agriculture and science.
He said such agreements, alongside Nato, the alliance with the US and the EU's SAFE loan defence programme formed Poland's overarching security strategy.
The country is also in discussions with Germany about closer cooperation, including on military matters, Tusk added.
The British weekly The Economist noted that as Poland grows wealthier and more influential, it will increasingly expect to be among Europe's main decision-makers.
(ał)
Source: PAP, IAR