My honest answer? It depends on the height, but in most cases a standard outdoor bench is too low for a true high table. Most outdoor benches have a seat height around 17 to 19 inches, which is designed for standard dining tables around 28 to 30 inches tall. A true high table—especially a bar-height table at 40 to 42 inches—needs seating that sits roughly 28 to 30 inches high. That is a big gap. If you put a regular low bench at a bar-height table, you will feel too low, your arms will not be in a comfortable position, and your legs will not fit naturally under the table.
That said, there are exceptions. If your high table is actually counter height at 34 to 36 inches, you need a seat height around 24 to 26 inches. Some outdoor benches are built taller for this exact purpose. They are often called counter height outdoor benches, high-top outdoor benches, or bar-height outdoor benches. So if your bench seat height is within about 10 to 12 inches of the tabletop, it can work well.
If you already own both pieces, measure first. A quick rule I use is: table height minus seat height should be around 10 to 12 inches for comfortable dining. For a 40-inch bar table, look for a bench with a seat height around 28 to 30 inches. For a 36-inch counter table, a bench around 24 to 26 inches works. If your outdoor bench is only 18 inches high, adding a cushion will not realistically fix an 8 to 12 inch height gap. A thick stack of cushions tends to shift, looks messy, and is not safe for outdoor dining.
Comfort matters too. High seating really benefits from a footrest. Many outdoor bar-height benches have a built-in foot rail or rung, which keeps your legs from dangling and makes longer meals more comfortable. If the bench does not have one, check whether you can add a stable separate footrest. Seat depth also matters. A deeper bench, around 17 to 20 inches, gives better support, especially when there is no backrest.
So yes, an outdoor bench can be used as a dining seat with a high table only if it is the right height. A standard low bench is not a good choice for a bar-height table. But if you buy or already own a taller bench and follow the 10 to 12 inch rule, it can look great and save space on a patio or deck. If you are shopping, search for outdoor bar bench, high-top bench, or counter height outdoor bench to get the proportions right.