Currently this can only be done via accessibility settings on iOS 13, as you could on previous versions of iOS. However it doesn’t look right.
Hopefully with the release of iOS13 to the public, Monzo can deploy a true dark mode to the app, would look really cool. Not sure about Android though.
Have you tried turning the brightness down?
The iOS13 option doesn’t change how Monzo looks unfortunately. (I’m on the public beta and just checked).
Dark mode will only change Apple’s apps for now. Third party apps need to be built for iOS 13 to see if the system Dark mode is on or not - and they’re not allowed to release iOS 13 apps to the store yet.
To be honest I don’t see Monzo making the effort to build for dark mode. They’ve done everything so custom-made and un-iOS-like that it’ll probably be a ball ache to do.
Edit: apparently I’m a cake boy today.
Happy cake day! 
Wait what there’s a forum darkmode… awesome just turned it on.
I personally don’t like white backgrounds and I find dark backgrounds easier for my eyes too. Anything from Dark to light grey or even a dark blue colour would be brilliant.
I’ve read apps on Android will be forced dark when a dark mode isn’t made for them after the release of Android Q. So it will be a case of make a dark mode or let Android force it and risk your design looking messy
An example of how the Monzo app looks when forced dark on Android Q is here; We're working on a new look for the Monzo app
That actually looks really cool. Looking at the devolpment docs, Google are making this easier too so shouldn’t be that hard to make the tweaks required 
Would also love a dark mode.
The new UI design looks great, but there’s a lot of white space.
There’s some great dark mode examples from Telegram and Dark Noise that I think could work well in a Monzo app.
I’m not sure if that’s just a standard response to any “does it include X” question?
Dark mode would definitely make sense with the introduction of iOS 13 featuring a system wide dark mode as well as support for developers.
Same with Android 10. And while you can force dark mode onto apps that don’t support it (including the Monzo app), the results can vary visually. In-app support is best.
Having upgraded to iOS 13 this evening the fact that Monzo has no dark mode sticks out like a sore thumb. Monzo purports to value UX highly so I would expect Monzo to have sorted this in time for the new update. Hopefully it will be coming along soon 
Yeah this has become a lot more important now we finally have Dark Mode on iOS. Monzo is an app people use daily, like Facebook (for which they’ve already confirmed Dark Mode is coming), WhatsApp, Instagram, Slack, Tinder etc. Dark Mode support is a must.
A bit harsh? A Twitter team hinting at something is hardly a statement of intent. If it doesn’t happen, it’s not really evidence of an intention to deceive. IMO
Edit: The current iOS version is 2.65 released a week ago.
Edit 2: Version 3.0 is now available.
Apologies, I was joking but should have realised that wouldn’t come across.
Clearly I jumped the gun, didn’t do my research and was simply wrong.
That’s fine. I’ve been guilty of that myself on more than one occasion. 