Three years ago, he fled his native Belarus after President Alexander Lukashenko's crackdown on protests following an election.
An election that supporters of opposition leader Sviatlana Tsikhanouskaya believe she won.
Last year, when Russia invaded Ukraine, Maryeuski felt the call to battle, and joined a Belarus volunteer unit fighting in support of Ukraine at the front.
"At first I thought about Ukraine, about Ukrainians and about protecting life. Then I thought about Belarus because I understood that if Russia loses the war, internal processes in the country will begin, which could be called a struggle for power or a struggle for survival. If the Russian elites begin fighting among themselves, who will take power after losing the war?"
If Russia loses, this could mark a significant change in Belarus.
And Maryeuski, along with his fellow veterans of the Ukraine conflict, are bound to play a role in the fight for their own country.
"I see this as an opportunity for us Belarusians to return home. Plus the fact that we are in Ukraine gaining experience, this will most likely be useful to us in Belarus because 2020 showed that protesting with flowers and white socks left on the benches gives you nothing."
A small but growing number of activists are saying now is the time to train for a real fight.
But it's not just the physical fight, but political, that the opposition are prepared to undertake.
Three years on from the election her followers believe she won, Tsikhanouskaya has all the trappings of a leader in waiting.
She has a cabinet in exile, diplomatic missions and regular meetings with Western dignitaries.
Her status is no small feat, considering Belarus opposition likely comprises a few thousand out of the 100,000 estimated to have left the country.
Many face lengthy sentences for criminal charges in absentia should they return to Belarus.
While they are divided over tactics, and their politics range from liberalism to nationalism, they are united by their desire to end Lukashenko's near three-decade rule.
They feel deep anger at his jailing and torturing of thousands of opponents, and his close alliance with Russia - which they say negates Belarus's sovereignty.
Opposition activists continue to build a covert network; they maintain over 20 alternative embassies and consulates for Belarusians abroad.
They run at least two intelligence bodies, help Belarusians escape the country, and hackers are developing apps that allow safe communication within Belarus.
However, most see a quick victory over Lukashenko as highly unlikely.
