Attorney General Dominic Grieve earlier on Wednesday told a Parliamentary committee that the U.K. was obliged to follow the judgment, and could face lawsuits from prisoners if it did not.
But Cameron later told lawmakers he had no intention of complying. "No one should be in any doubt. Prisoners are not getting the vote under this government," he said.
The European Court of Human Rights ruled in 2010 that Britain must overturn a centuries-old law and allow prisoners to vote in national elections.
At the time, Cameron said the decision had made him feel "physically ill."