Washington: In a prime-time announcement worthy of a Bachelorette rose ceremony - or, closer to home, a season finale of The Apprentice - US President Donald Trump revealed he had selected conservative federal appeals court Judge Brett Kavanaugh as his nominee for US Supreme Court Justice.

If Kavanaugh is confirmed by the Senate, where Republicans hold a wafer-thin majority, Trump will lock in a 5-4 conservative majority on the nation's most powerful court, an outcome Democrats argue could lead to a roll-back of access to abortion, gay rights and protections for racial minorities.

Democratic leaders in Congress - still furious at the Republicans for "stealing" a Supreme Court seat from them in 2016 - immediately signalled they would fight ferociously against Trump's choice, but their prospects of success look slim.

Trump's decision was greeted with almost unanimous praise from Republican senators and conservative activists, who are delighted at the prospect of controlling the Supreme Court for decades.