The US Supreme Court has quashed President Donald Trump’s last-ditch effort to keep the White House by rejecting a lawsuit that sought to undo the results of the Nov 3 elections.

"The […] motion for leave to file a bill of complaint is denied for lack of standing under Article III of the Constitution,” the court wrote in a decision announced on Friday evening. “All other pending motions are dismissed as moot.”

The decision almost ensured that Trump’s Democratic rival Joe Biden will take oath as the 46th US president on the inauguration day, Jan 20.

Filed by Texas Attorney General Ken Paxton, the lawsuit sought to invalidate 10 million votes in four battleground states — Pennsylvania, Georgia, Michigan, and Wisconsin — that President Trump lost. Seventeen of the 50 US states and 120 Republican lawmakers were also backing this move.

“Texas has not demonstrated a judicially cognisable interest in the way another State conducts its elections,” the Supreme Court wrote, adding that it was denying the complaint for “lack of standing”.

Reacting to the decision, Trump took to Twitter to express his disappointment early Saturday, once again claiming incorrectly that the election was rigged.

"The Supreme Court really let us down. No Wisdom, No Courage," he tweeted hours after the court decision.

"So, you’re the President of the United States, and you just went through an election where you got more votes than any sitting President in history, by far – and purportedly lost," he wrote in another tweet.

Although President Trump has been trying to overturn the votes since the election day, this is the latest and most significant legal defeat for him and his allies so far.

On Wednesday, Trump had said the case by Texas was the "big one", hoping for a decision in his favour. "We will be intervening in the Texas (plus many other states) case. This is the big one. Our country needs a victory!"

Paxton's motion asked justices to extend the deadline for election certification to Dec 14, giving time to investigate alleged voting irregularities in the four states. Seventeen other states also filed a brief in the Supreme Court in support of Texas. These included Alabama, Arkansas, Florida, Indiana, Kansas, Louisiana, Mississippi, Montana, Nebraska, North Dakota, Oklahoma, South Carolina, South Dakota, Tennessee, Utah, and West Virginia – states that Trump won in 2020.

Minority Leader Kevin McCarthy and Minority Whip Steve Scalise in the US House of Representatives also backed the move along with a bunch of Republican lawmakers.

The four states targeted by Paxton had until Thursday afternoon to respond.

"The challenge here is an unprecedented one, without factual foundation or a valid legal basis,” Michigan wrote in its response.

Pennsylvania said the lawsuit was a "seditious abuse of the judicial process" and pleaded for the court to "send a clear and unmistakable signal that such abuse must never be replicated".

Georgia, the most disputed among the battleground states, wrote: "Texas’s claims are no different than the multiple cases pressed in state and federal courts in Georgia over the past weeks. […] And none of that litigation has gone anywhere.”

Pennsylvania, which has the highest number of electors – 20 – among the disputed sates, wrote: “Nothing in the text, history, or structure of the constitution supports Texas’s view that it can dictate the manner in which four sister States run their elections, and Texas suffered no harm because it dislikes the results in those elections.”

Even Ohio, a state President Trump won, opposed Texas’s motion. “The relief that Texas seeks would undermine a foundational premise of our federalist system: the idea that the States are sovereigns, free to govern themselves,” it wrote.

Lower courts have already dismissed dozens of lawsuits and appeals by the Trump campaign, forcing the president and his supporters to pin their hopes on the Supreme Court.

Earlier Friday, Trump urged the Supreme Court to entertain the lawsuit. “If the Supreme Court shows great wisdom and courage, the American people will win perhaps the most important case in history, and our electoral process will be respected again,” he tweeted.

The president has said that they were seeking to overturn the results because the elections were rigged massively. But US Attorney General Bill Barr, a Trump appointee, said earlier this month that the Department of Justice has not yet seen any evidence of widespread voter fraud.

A growing number of Republicans had also acknowledged Trump’s loss.