Lawyers for Abu Zubaydah, a 42-year-old Palestinian, and Saudi Arabian national Abd al-Rahim al-Nashiri, 48, told the court that Warsaw authorised the US intelligence agency to detain their clients in Poland for several months in 2002-03.
They were repeatedly tortured by waterboarding during that time, the lawyers alleged.
They also alleged that the Polish authorities failed to act when the two men were transferred to Guantanamo in 2003, where they remain a decade later without ever having been put before a judge.
Singh said al-Nashiri was kept naked, made to witness mock executions and threatened that his mother would be brought and sexually abused in front of him.
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The court said it would deliver a ruling but did not give a date.
The lawyers argued that Poland failed to uphold its commitments under the European Convention of Human Rights by allowing the two men to be made victims of inhuman or degrading treatment, by allowing them to be illegally deprived of their liberty and by failing to properly investigate the men's treatment.
Mikolaj Pietrzak, another lawyer for al-Nashiri, said the Polish state had done nothing for five years and had not cooperated with a probe by a Council of Europe investigator, Swiss politician Dick Marty, into the so-called "war of terror" operations in Europe.
Poland is one of a number of European countries that have been accused of assisting the United States in the process of extraordinary rendition of suspected terrorists from the Middle East, Pakistan and Afghanistan to the controversial facility at Guantanamo.
The ECHR ordered Macedonia to pay el-Masri 60,000 euros (USD 81,000) in damages.