"I've handed over my papers, that's right," Tusk told reporters in Warsaw when asked whether he had tendered his resignation to the president.
He is likely to be replaced by Ewa Kopacz, dubbed his loyal "Iron Lady" by Polish analysts.
Brussels's choice of Tusk to succeed Herman Van Rompuy in the key EU job is seen in Poland as not only a nod to him, but also a sign of the country's growing political and economic importance within the European fold.
But it still remains to be seen whether the "Tusk effect" will rub off on the party in legislative elections scheduled for the autumn of 2015.
Tusk, 57, earned the distinction of steering Poland through the global financial crisis as the only European Union member to maintain growth.
As prime minister he also fostered cosy ties with Poland's neighbour, EU powerhouse Germany, in the wake of a frosty earlier episode under a PiS administration.
Once President Bronislaw Komorowski accepts the resignation, he will have two weeks to designate a successor before a September 25 deadline but the president could select a candidate before he makes a trip to Netherlands and the US starting on September 20.
The governing coalition -- an alliance between Tusk's PO and the agrarian Polish People's Party (PSL) -- has already nominated Kopacz, the current parliamentary speaker and an unwavering Tusk ally.
She is highly likely to get the green light from parliament, given the extent of her backing there.
