Tusk, the sole candidate, received 16,316 valid votes in favour out of 16,695 cast.
The result was announced on Monday by Deputy Speaker of the Sejm lower house of parliament Dorota Niedziela, who oversaw the election process.
Turnout stood at 78 percent of eligible, dues-paying members.
Sunday's vote was the first leadership election since the Civic Platform (PO) merged with the smaller Modern (Nowoczesna) and Initiative Poland (Inicjatywa Polska) parties under the KO banner in October last year.
Tusk first won a membership-wide vote in 2013, defeating centre-right conservative Jarosław Gowin.
He was later succeeded by Grzegorz Schetyna and then Borys Budka, before returning to the leadership in 2021 with 97 percent support and going on to become Prime Minister following parliamentary elections.
(ał)
Source: PAP