Can I connect a newly bought Apple Watch series 3 to my iPhone 6?

A new bought Apple Watch will have watchOS 6 preinstalled, so your phone has to be running iOS 13.

But, Apple Support might be able to downgrade your watchOS, if you contact them and explain your situation.

You're welcome 🙂

If the watch has software version watchos6 then it will NOT pair with an iphone 6,watchos6 requires an iphone with ios13 or higher an iphone 6 will only update to ios12,for ios13 you need an iphone 6s or higher.If the watch has watchos5 or below then it WILL pair.