"Amy Coney Barrett, confirmed," the House judiciary GOP page tweeted, shortly after Ms Barrett, 48, was sworn in on the high court in America. "Happy Birthday, Hillary Clinton," the post mockingly added.
Former secretary of state Clinton, who turned 73 on Monday, had condemned the appointment of Ms Barrett to the bench, saying it signalled the death knell for the Affordable Care Act (ACA), sweeping health reforms ushered in under the Obama administration.
"Senate Republicans just pushed through a supreme court justice who will help them take away Americans' health care in the middle of a pandemic," Ms Clinton said of the appointment.
"For them, this is victory," she added, before urging Americans to vote against both House and Senate GOP candidates in November's election.
GOP lawmakers secured a huge partisan victory for president Donald Trump last night by appointing Ms Barrett to the court with just over a week to go until election day.
The vote, a mere formality, was conducted along party lines, with Republicans securing a 52-48 win. Maine senator Susan Collins was the only GOP rebel.
Ms Barrett, an academic and former appeals court judge, was installed in the supreme court with lightning speed as Republicans raced to confirm her before the 3 November poll.
She becomes only the fifth women justice to sit on the court and replaced Ruth Bader Ginsburg, who died in September following a cancer diagnosis. Mr Trump has now appointed three justices to the court.
The appointment of Ms Barrett, a pro-life Catholic, is likely to boost the electoral prospects of GOP candidates running in states that have large numbers of Christian voters.
On a national level, evangelical Christians makeup around a quarter of the US electorate and could have a big say in deciding who enters the White House. They were key in Mr Trump's 2016 victory.
Ms Barrett's appointment solidifies a 6-3 conservative-leaning majority on the highest court in the land, which threatens to have implications for some of the most hotly contested issues in America, such as abortion and healthcare, which Ms Clinton alluded to.
During Senate hearings earlier this month, Ms Barrett dodged questions on how she might rule on both the ACA - which provides affordable health insurance to millions of Americans - and the landmark 1973 ruling Roe v Wade, which made abortion legal.
She could start work as early as next week.