US President Joe Biden has reversed a ban on federal funds going to international aid groups that perform or inform about abortions.
He said the ending of the so-called Mexico City Policy reverses former President Trump's "attack on women's health access".
The memo orders a review of a Trump-era policy blocking funding for US clinics that offer abortion referrals as well.
Mr Biden also signed an edict expanding the Obamacare insurance programme.
"I'm not initiating any new law, any new aspect of the law," he said in the White House Oval Office on Thursday, responding to criticism that he was governing by executive order, rather than congressional legislations.
"There is nothing new that we're doing here other than restoring the Affordable Care Act ... to the way it was before Trump became president," he added.
What is the global abortion 'gag rule'?
The Mexico City Policy was first enacted by Republican President Ronald Reagan in 1984 and has been repeatedly renewed by Republicans and cancelled by Democrats.
For decades, the US has barred money from being spent on overseas abortions but the Mexico City policy takes that a step further. It prevents federal funds from going to organisations that provide abortions, abortion counselling or advocate for the legal right to abortion.
The programme was expanded under Mr Trump, who banned funds from going to non-governmental organisations (NGOs) that themselves provide funding for abortion groups.
In a statement earlier, the White House said Mr Biden was issuing the presidential actions "to support women's and girls' sexual and reproductive health and rights in the United States, as well as globally".
A report by the US Government Accountability Office released last year found that in 2017, NGOs were unable to receive around $153m (£112m) because they chose not to cut back on abortion programmes.
The report found 54 occasions in which NGOs did not accept US funds due to the policy.
What else has Biden done on abortion?
Mr Biden has also instructed the US health department to immediately consider removing Trump-era restrictions to a domestic family planning programme for low-income Americans known as Title X.
Mr Trump's overhaul of the Title X programme saw tens of millions of dollars stripped from any health centres that offered or referred patients for non-elective abortions, like Planned Parenthood.
Mr Biden on Thursday also removed the US from a 2020 resolution known as the Geneva Consensus, a non-binding charter of more than 30 countries that oppose abortion.
The actions to begin undoing Mr Trump's abortion and healthcare legacy comes on the eve of the annual anti-abortion March for Life protest, which is being held virtually on Friday. In 2020, Mr Trump made history by becoming the first sitting US president to appear at the rally.
It also comes amid legal battles over abortion, as several mostly Republican southern states pass local regulations that drastically cut back access to the procedure.
Conservatives are newly emboldened to try to reverse 1973's Roe v Wade landmark Supreme Court decision, which legalised abortion across the US, after Mr Trump appointed judges who have tilted the court in conservatives' favour.
Some Democrats have called for Congress to end the so-called Hyde Amendment, a federal provision that says funds cannot go to abortion programmes in US states except in cases of rape and incest. Republicans have vowed to block spending legislation that does not include it.
Mr Biden had long supported the Hyde Amendment as a senator and vice-president, but withdrew support during the 2019 Democratic primary elections.
What's happening with Obamacare?
Mr Biden on Thursday signed an order to reopen the Affordable Care Act - also known as Obamacare - federal insurance marketplace for three months.
Under Mr Trump, the enrolment period lasted just six weeks, as the Republican administration sought to dismantle the programme.
Mr Biden said that with the ongoing "Covid crisis", now was the time to reinstate access to healthcare and affordable programmes.
Democratic Speaker of the House Nancy Pelosi praised the expansion in a weekly briefing, saying: "We're very excited about that because we're of course in the middle of a pandemic and we see this was a matter of life and death."
Mr Biden's directive also mandates agencies look into policies that may reduce coverage in the Medicaid healthcare programme for low-income Americans. This includes a measure created under the Trump administration that allows states to impose work requirements on aid-seekers.
The president has also ordered a re-examination of policies that hurt protections for patients with pre-existing conditions and any measures that undermine the federal insurance marketplace or enrolment.
Because most Americans receive health insurance from their employers, pandemic-related layoffs have led to a spike in uninsured people in the past year.
Early estimates say that an additional five to 10 million Americans have lost their health insurance due to coronavirus, but official government studies of the issue are not due until later this year.