A last-minute compromise deal led to the easy passage of the EU's reform treaty. The government and opposition had been locked in weeks of feuding over the Lisbon Treaty, which replaces the failed EU constitution.
The document has to be ratified by all 27 EU member states if it is to take effect by the 2009 target.
There were worries that Poland, which nearly derailed earlier European treaty negotiations, would vote it down. In Poland, the treaty required approval from two-thirds of parliamentarians to pass, and the euro-skeptic Law and Justice Party had expressed strong reservations.
Pro-EU parties needed a supermajority
But in the end, the Law and Justice Party threw their support behind the treaty. Liberal Prime Minister Donald Tusk and President Lech Kaczynski worked out a compromise two days before the vote and then jointly campaigned for their followers to go along. All told, 384 members of parliament voted in favor of the treaty and 56 voted against it.
As part of the compromise, Tusk agreed to start working on new legislation that would amend the divisions of power between the president, government and parliament.
Kaczynski and Tusk hailed the treaty as good news for both Poland and Europe.
"Poland needs Europe and Europe needs Poland," Tusk said, quoting Polish Pope John Paul II.
While ratification is now largely assured, the Senate is set to consider the bill on Wednesday and could approve it the same day. It will then go back to Kaczynski for final approval.
The treaty, adopted by EU leaders in December, is designed to streamline the way the bloc is run. It has already been ratified by lawmakers in Bulgaria, France, Hungary, Malta, Romania and Slovenia.