Can You Sit on the London Eye on New Year's Eve?
Almost certainly not during the fireworks, and the reason is structural: on the night itself the wheel is the launch platform, not the viewing platform.
Not during the fireworks, no. The confusion is understandable, because the London Eye is the single most photographed object of the whole display, but the reason it appears in every shot is exactly why nobody is inside it. On the night, the wheel is the firework launcher.
The Mayor of London's New Year's Eve display is fired at midnight on 31 December from the London Eye itself and from barges moored beside it on the Thames. It runs somewhere between ten and fifteen minutes. A structure rigged with pyrotechnics and being fired at midnight is not simultaneously running a passenger rotation, so the sequence of events people imagine, a capsule at the top of the wheel while the sky goes off around it, is not something you can buy a ticket for.
What you can actually buy for the night
The riverside viewing areas have been ticketed since 2014 rather than open to anyone who turns up. Gates open at 8pm and only ticket holders get into the viewing area, which is a meaningful detail if the plan was to wander down to the South Bank at eleven. Those tickets are also not sold by the attraction. The London Eye's own site is explicit that it does not sell them directly and points people to the Mayor of London's official channel instead.
That leaves three broad options on the night, and none of them is a ride: a ticketed spot in a riverside viewing area, a boat on the water, or a free vantage point further out where the display is smaller but nobody is checking wristbands.
Earlier on 31 December
This is where the honest answer gets less satisfying. Daytime rides on 31 December are a different question from the fireworks, and the operator does not publish a firm answer far in advance. Third-party ticket resellers regularly list a shortened day on New Year's Eve, closing in the mid-afternoon so the site can be cleared and prepared. That is plausible and consistent with how the evening works, but it is not something the official opening-hours page commits to in writing months ahead, and it has varied between years.
So the reliable advice is unglamorous: if you want to ride on 31 December itself, check the official site for that specific year's hours before you plan anything around it, and expect a short day rather than a normal one. If you want to be there for the display, buy a fireworks ticket through the Mayor of London's channel and treat the wheel as scenery.
The other thing worth knowing is what happens next. The Eye closes for annual maintenance through January. A trip built around a New Year ride has a narrower window than most people assume, because the days immediately after the first are close to the end of the operating year.
The one New Year's Eve it really was about
There is a neat irony buried in this question. The wheel was ceremonially opened on 31 December 1999, deliberately timed to mark the millennium, and that night is the entire reason it was christened the Millennium Wheel and the reason this domain carries that name. It was the most New Year's Eve any structure in London has ever been.
Nobody rode it. The ceremony went ahead but the wheel did not carry passengers that night. The first passengers boarded on 1 February 2000, and the public opening slipped to 9 March after a fault in a capsule clutch. So even on the single New Year's Eve the London Eye was built for, the answer to "can you sit on it tonight" was no.
The version of this that does work
If the real want behind the question is a celebratory evening ride with a drink in hand and the city lit up, that exists, it just is not tied to 31 December. The Champagne Experience runs the standard 30-minute rotation with fast-track priority boarding, a wait in the Eye Lounge rather than the main queue, a personal host and a glass of chilled Moet & Chandon Imperial Brut in the capsule. It is the highest-rated ticket tracked on this site at 4.9 across 896 reviews, and it currently shows as likely to sell out on the listing.
Booked on a clear evening in late December, with London's sunset falling before 4pm, you get the lit skyline for the whole rotation and none of the crowd management that comes with the last night of the year. It is a substitute rather than the same thing, but it is a bookable one.
One last point to keep the two things separate in your head. Any New Year's Eve access, whether a viewing-area ticket or something the attraction chooses to run in a given year, is arranged and sold entirely apart from the standard and combo tickets tracked here. None of those five includes fireworks access, and no amount of upgrading between them changes that.