The Abbott government will soon make two very significant appointments. They arise due to the retirements of Justices Kenneth Hayne and Susan Crennan from the High Court. The Constitution mandates that High Court judges must retire at 70, the so-called "statutory age of senility", which for Hayne is on June 5 and Crennan on July 1 next year.

The seven judges of the High Court have the final say on key aspects of the law. In recent years they have issued decisive rulings on the Gillard government's Malaysian plan, NSW political donation laws, the national schools chaplaincy program and Western Australia's Senate election. It was also the High Court that first recognised native title and in the years to come it may determine, for example, that Australian law incorporates a right to privacy.

Retiring: Justice Susan Crennan (centre) will leave the High Court in February. Credit:Chris Lane

Not surprisingly, every government wants to influence how such matters are decided. They do so by carefully selecting the people who sit on the court. This provides an opportunity not only to influence Australian law and politics in the short term, but for many years after. Prime Minister John Howard's last appointment to the court, Justice Susan Kiefel, was selected just before the 2007 election and need not retire until 2024.

The Abbott government must appoint a new High Court judge sooner than expected. Crennan will leave the court early on February 2, meaning that the announcement of Australia's 51st High Court justice is imminent. The government cannot afford to wait much longer, lest Crennan's replacement be unable to take up their duties immediately on her departure.