After days of frenzied lobbying and speculation, President Donald Trump has decided on federal appeals Judge Brett Kavanaugh for his second nominee to the Supreme Court.

It sets up a ferocious confirmation battle with Democrats as he seeks to shift the nation’s highest court further to the right.

Mr Trump chose Mr Kavanaugh to replace retiring Justice Anthony Kennedy.

With customary fanfare, Mr Trump planned to unveil his choice on prime-time TV. His final options were all young federal judges who could help remake the court for decades to come with precedent-shattering rulings on issues such as abortion, guns and health care.

Top contenders had included federal appeals judges Raymond Kethledge, Amy Coney Barrett and Thomas Hardiman, as well as Mr Kavanaugh, who is currently a federal appellate judge in the District of Columbia.

Relishing the guessing game beyond the White House gates, Mr Trump had little to say about his choice before the announcement.

Some conservatives have expressed concerns about Mr Kavanaugh – a longtime judge and a former clerk for Mr Kennedy – questioning his commitment to social issues like abortion and noting his time serving under President George W Bush as evidence he is a more establishment choice.

US Judge Brett Kavanaugh speaks after being nominated by US President Donald Trump. Photo: Getty

He was also one of the lead authors of the Ken Starr report into President Bill Clinton.

But his supporters have cited his experience and wide range of legal opinions.

With Democrats determined to vigorously oppose Mr Trump’s choice, the Senate confirmation battle is expected to dominate the months leading up to November’s midterm elections.

Senate Republicans hold only a 51-49 majority, leaving them hardly any margin if Democrats hold the line. Democratic senators running for re-election in states Mr Trump carried in 2016 will face pressure to back his nominee.

Mr Kavanaugh is likely to be more conservative than Justice Kennedy on a range of social issues. At the top of that list is abortion.

A more conservative majority could be more willing to uphold state restrictions on abortion, if not overturn the 45-year-old landmark Roe v. Wade decision that established a woman’s constitutional right.

Mr Kennedy’s replacement also could be more willing to allow states to carry out executions and could support undoing earlier court holdings in the areas of racial discrimination in housing and the workplace. Mr Kennedy provided a decisive vote in 2015 on an important fair housing case.

Mr Trump is hoping to replicate his successful nomination of Justice Neil Gorsuch last year.

The president has spent the days leading up to his announcement discussing the pros and cons of various contenders with aides and allies.

In addition to Mr Kavanaugh, in recent days he expressed renewed interest in Mr Hardiman, the runner-up when Mr Trump nominated Mr Gorsuch, said two people with knowledge of his thinking.

-AAP