Donald Trump's nomination of Brett Kavanaugh to the Supreme Court is shaping up to be the most consequential decision of his presidency.

Conservative, savvy and educated, Judge Kavanaugh played a role in just about every major political battle of the 1990s.

And he is to become even more powerful when Justice Anthony Kennedy retires at the end of this month, giving him a say in some of the major issues in US politics: abortion, gun rights, partisan gerrymandering and affirmative action.

The US president's pick to join the Supreme Court is pro-business, reliably conservative and brings a strong Republican pedigree to the position.

His predecessor Justice Kennedy served as the swing vote on the country's highest court for the last decade.

With four conservatives and four liberals either side of him ideologically, Justice Kennedy cast the deciding vote on a series of divisive issues - most famously paving the way for the legalisation of same-sex marriage.

Mr Trump has already placed one conservative on the court, with Neil Gorsuch confirmed early in his presidency after the death of Antonin Scalia.

The next justice to be appointed to the Supreme Court will shape US law and the lives of its citizens for decades to come, with any Mr Trump appointee set to push the balance of the court 5-4 to conservatives.

So who is Brett Kavanaugh and why is his nomination so important?

WHY DOES IT MATTER?

Supreme Court justices are appointed for life and only leave the bench if they retire or die.

Emma Shortis, Research Officer at RMIT University's EU Centre, agreed the nominations of Judge Kavanaugh and Justice Gorsuch may end up being the most significant act of Mr Trump's presidency.

"It's really important for a few reasons," Ms Shortis told 9news.com.au.

"One of them is the Supreme Court has the final say on a lot of issues in American politics.

"So if Congress passes some legislation, it can get tested at the Supreme Court and the Supreme Court can decide if it's constitutional or not constitutional.

"So it has implications basically across all aspects of American life for that reason.

"They can have an impact for generations because they sit on the bench for so long."

Justice Kennedy was regarded as something of a centrist and often cast the deciding vote on divisive issues.

His vote wasn't always predictable - conservative on issues such as gun rights and religious liberty but progressive on same-sex marriage - and meant the court rarely leaned a particular way ideologically.

But his retirement will likely leave Chief Justice John Roberts as the deciding vote, with a Mr Trump appointee to shift the balance to conservatives.

That could shift US policy for generations on hot-button issues such as abortion and affirmative action.

"For those issues that are really important to conservatives such as abortion, the sense of it is and the hope from the conservative side of politics is he will turn the Supreme Court conservative," Ms Shortis said.

"It has implications for abortion and people are rightly focusing on that, but it also has implications for lots of other areas of politics including things like campaign financing, which the Supreme Court has a big influence on."

Mr Trump appears fully aware of the consequences of his decision, teasing the announcement of his nominee in his typical reality television style.

The importance of a Supreme Court nomination was underscored in the final year of Barack Obama's presidency.

Mr Obama nominated Merrick Garland to replace the late Justice Scalia, but Senate Republicans refused to even hold confirmation hearings given the looming 2016 presidential election.

Rightly or wrongly, the move worked and allowed Mr Trump to appoint the conservative Justice Gorsuch.

'THE FORREST GUMP OF REPUBLICAN POLITICS'

Judge Kavanaugh, 53, was born in Washington DC and raised in Maryland. He brings a strong Republican pedigree.

The Yale graduate worked as a clerk for Justice Kennedy but entered the broader public consciousness with his role in the Starr Report into alleged wrongdoing by then-President Bill Clinton.

Mr Kavanaugh was the principal author of the infamous document, which detailed independent counsel Kenneth Starr's investigation of the Whitewater land deal, the suicide of deputy White House counsel Vince Foster and the Monica Lewinsky affair.

He later served as part of George W. Bush's 2000 presidential campaign, which ended with the Supreme Court deciding the election in the Republican's favour after a recount in Florida.

Judge Kavanaugh was nominated to the District of Columbia Circuit Court of Appeals in 2003, but his confirmation was bitterly contested in the Senate for three years.

Democratic Senator Dick Durbin famously described Judge Kavanaugh as "the Forrest Gump of Republican politics" for his ability to pop up in the highest profile stories of the decade.

Judge Kavanaugh was eventually confirmed in 2006 and has served on the court since.

He is a Catholic and has two children with wife Ashley Estes, whom he met while working in the Bush White House as legal counsel to the president.

WHAT DOES IT MEAN FOR ABORTION RIGHTS?

As soon as news of Justice Kennedy's retirement broke, one issue above all others came into sharp focus: abortion rights.

Overturning Roe v. Wade, the 1973 Supreme Court ruling which declared abortion was a woman's right under the US constitution and prohibited states from banning them, has been a goal of conservatives for decades.

Many states have chipped away at abortion legislation in such a way that effectively prohibits abortions, but the shift to a conservative majority on the bench could now see the landmark ruling overturned.

"In a lot of states, access to abortion is extremely limited and particularly conservative states have taken steps to limit that access, be it through de-funding or working their way around the law in that sense," Ms Shortis said.

"(Roe v. Wade) wouldn't have to be overturned, but that has been an aim of conservatives and the evangelical right-wing of the Republican Party.

"That's been an aim for a long time, that group of people see themselves as being on the right side of history and will campaign to have it overturned.

"And if it is overturned, that has huge implications because lots of states have sunset clauses so that if Roe v. Wade is overturned, abortion becomes automatically illegal.

"That could have very, very vast implications for a lot of people."

Chuck Schumer, the Democrats' leader in the Senate, has vowed to oppose Judge Kavanaugh's confirmation and claimed he was picked because of his stance on reproductive rights.

"Judge Kavanaugh got the nomination because he passed this litmus test, not because he'll be an impartial judge on behalf of all Americans," he wrote on Twitter.

"If he were to be confirmed, women's reproductive rights would be in the hands of five men on the Supreme Court."

CAN THE PRESIDENT FACE CRIMINAL PROSECUTION?

Judge Kavanaugh has alarmed Democrats with his writings on executive privilege, arguing a sitting US president should be exempt from criminal prosecution and civil suits.

"The President's job is difficult enough as is," Mr Kavanaugh wrote in 2009.

"And the country loses when the President’s focus is distracted by the burdens of civil litigation or criminal investigation and possible prosecution."

With special counsel Robert Mueller's Russia investigation ticking along, Democrats have claimed Mr Trump's pick is designed to protect himself.

Senator Durbin – he of the "Forrest Gump" jibe – was one of many Democrats to make that point.

WILL HE BE CONFIRMED?

Judge Kavanaugh still needs to be confirmed by the US Senate, which is narrowly controlled by Republicans with a 51-49 majority.

But moderate Republicans Susan Collins and Lisa Murkowksi, who are pro-abortion rights and have signalled their concern with appointing a justice who will overturn Roe v. Wade, could prove a stumbling block.

Republicans need 50 votes to confirm the appointment, so assuming all Democrats oppose Judge Kavanaugh, either female Senator's votes could sink the nomination.

What happens in the Senate will shape the lives of Americans for generations.

"If Kavanaugh is confirmed, this will have huge implications for women's rights and abortion rights but also things like gun control, campaign financing and also if the Muller investigation proceeds and gets as far as the Supreme Court, it could have huge implications there," Ms Shortis said.

"It's a far-reaching and wide-ranging issue and we don't know how it will play out."