Australia's High Court has ended a hearing on whether the deputy prime minister will be disqualified from Parliament for breaching a constitutional ban on dual citizens becoming lawmakers, a verdict that could cost the government power.

The seven judges have heard three days of testimony ending Thursday in the cases of Deputy Prime Minister Barnaby Joyce and six senators who said they did not know they were dual nationals when they ran for election last year.

The constitution bans dual nationals from Parliament, a prohibition that critics have condemned as outdated in a country where almost half the people are immigrants or have an overseas-born parent.

Chief Justice Susan Kiefel acknowledged the cases were urgent, but did not indicate when she and her fellow judges would deliver their verdicts.