I'd start by checking to see if there's been tunneling under it from voles or a groundhog. Push on the soil under the shrub. Often sudden wilting indicates some type of sudden change in roots.

I'd also check the soil moisture and if it's dry, water long and slow from something like a trickling hose. Much of the NE part of the US has been unusually dry, and the soil conditions in different parts of your yard and neighborhood may be different enough that this plant is suffering more from the drought than others nearby.

Look for damage to the bark or lower trunk from insects, yard equipment, sapsuckers, etc.

If you can't find any specific cause, Prunus are susceptible to a large number of diseases, so removal may be needed. If it's a plant you like, I'd probably wait until next spring to see whether it leafs out normally.

Remove it. Ornamental fruit trees are almost always an eyesore.

unless you just have a jones to use your saw ... then i would suggest waiting until spring to see if and how it buds out ...

full sun plant.. the shape of yours.. sure makes it look like it trying to grow out of too much shade ... which might mean tree root competition ...

you cant really compare 2 trees in your yard .. its not safe.. to presume they should act the same ... too many possible variables ... imo ...

they are short lived in tree time.. 10 to 20 years max.. is the usual ... ken

btw.. its october.. so its not really all that early of a leaf fall .. if this happened in say june.. then that is real early .. and i would question if it was viable ... ken

Floral, in most parts of the US (around me) they behave the same. This includes north carolina, south carolina, tennessee, and kentucky. I am not sure about the UK, or other more northern/tropical places.

Stuartlawrence - are you able to give us a closer view of the foliage? To me it looks as if it has withered quite quickly in situ rather than the normal gradual decline and dropping of Autumn leaves.

Logan-Caldwell - if you are not sure about other places (and plants) it would be sensible to avoid about making blanket statements about them.

Here's closeup photos of the leaves and a closeup of the trunk. The leaves have indeed wilted. There are much fewer leaves on the tree since the last photo. Most branches I snap look dead. The tree has been developing dead branches for years but I never thought anything of it.

Reguarding Logan's comment, here's a photo of the tree in the spring.

Get yourself a knife..start with the newest growth remove small chunk of bark see if its green under the bark..if not work your way down from newer growth to older growth. Don't remove any branches!

Are you positive I would see green? I broke off a live branch off of my other Flowering Plum Tree which is healthy and there is no green inside the branch, only some red. The branch also seems very flexible and hard to break. On the Plum tree that might be dead the branches snap pretty easily.

The red you see in the inner bark. The green will but under the inner bark its a thin layer sometime it can be hard to see if the trees are going dormant you won't see it

THE TREE IS DEAD!!! It wouldn't last much longer anyway, just an ornamental fruit.