Pricing has also been revealed - it will cost £5.99 per month or £59.99 a year, making it more expensive than the earlier DisneyLife platform.
Disney+ launched in the US and Canada in November, where it became the most downloaded app.
The new launch date may be an attempt to tackle piracy of shows like The Mandalorian, suggested one expert.
The other European countries that will receive Disney+ at the same time as the UK are Ireland, France, Germany, Italy, Spain, Austria and Switzerland.
The Netherlands already has access as it was used as a testing ground for the platform.
In the US, Disney+ costs $6.99 (£5.36) per month.
"The UK price was predictable given the aggressive US charge and the trend of a race to the bottom in terms of price - none of these services are going to make money for years," Tom Harrington at Enders Analysis told the BBC.
He added that executives may have been under pressure to bring forward their original plan because the firm wanted "to get The Mandalorian out there before even more people pirate it".
DisneyLife re-brand
Disney has confirmed that the new service will replace DisneyLife in the UK and Ireland.
The earlier streaming platform had been offered since 2015, and also offered access to Disney's library of cartoons and films, but excluded content including the Star Wars films, Marvel movies and National Geographic documentaries provided by its successor.
DisneyLife cost £1 less per month and also included access to ebooks and music, which are not bundled into the new package.
However, one advantage of the new service is that some content will be screened in 4K resolution, which was not the case before.
In the US, Disney+ also includes the back catalogue to The Simpsons cartoon series, which Disney acquired when it bought 21st Century Fox last year. However, it has not been confirmed if this will be offered to the UK or other European countries.
By comparison, Netflix's "basic" plan also costs £5.99 per month, but does not offer HD or 4K.
And Sky's Now TV service - which contains some Disney content - divides up films and TV shows into different packages and charges an extra £3 a month fee if users want to watch them in 1080p rather than 720p resolution.
Netflix is expected to announce financial results later today, which may reveal how much of an impact rising competition from Disney+ has had on the streaming giant's fortunes.
Disney+ will become available in Belgium, Portugal and Nordic countries in the summer of 2020.
