0218 GMT February 23, 2020
Mercury's sojourn between Earth and our star lasted from 11:12 until 18:42 GMT, reported BBC.
It was the third such pass of 14 this century; Mercury will not make another transit until 2019 and then 2032.
The event is impossible ― and dangerous ― to view with the naked eye or binoculars, but astronomy groups worldwide are offering the chance view it through filtered telescopes.
Live views from space and ground telescopes were also available online.
They showed Mercury as a tiny black circle, smaller but darker than many sunspots, slowly traversing the Sun's giant yellow disc.
Mercury spins around the Sun every 88 days, but its orbit is tilted relative to the Earth's. It is that discrepancy which makes it relatively rare for the three bodies to line up in space.
From western Europe, northwestern Africa and much of the Americas, Mercury's seven-and-a-half-hour glide across the Sun was visible in its entirety. A further swathe of the planet was able to catch part of the transit, depending on local sunrise and sunset times.
The only land masses to miss out completely were Australasia, Far Eastern Asia and Antarctica.
Because Mercury is so small ― just one-third as big as Earth and, from our perspective, 1/150th of the Sun's diameter ― its transit could only be glimpsed under serious magnification; the ‘eclipse glasses’ used by thousands of people to view last year's solar eclipse were useless.
And to avoid permanent eye damage, telescopes had to be fitted with a solar filter before being trained on the Sun. The British Astronomical Association explained on its website how amateur stargazers could enjoy the spectacle safely.
Professor David Rothery said the celestial event did not present any novel scientific opportunities ― but was special nonetheless.
"From this transit, we're unlikely to learn anything we don't already know," he said. "But what a wonderful event for showing people Mercury. It's a hard planet to see.
"Historically, transits were of immense importance."