Discounting all products in WooCommerce sounds like it should be a single button, a master discount switch you flip when a sale begins and flip back when it ends. Well, it isn't, at least not natively.
But there are approaches that get you close to that level of simplicity, and some are significantly better than others depending on how large your catalog is and how precisely you want to control the promotion.
The Obvious Approach and Why It Doesn't Scale
The most direct way for you to discount all products in WooCommerce is to edit each product and set a sale price.
This works on a small scale if you have only a handful of products and a couple of minutes for editing. But for a catalog of any meaningful size, this is a genuinely impractical approach.
WooCommerce offers a bulk price-editing option in the Products list view. You can select all products, choose Edit from the bulk actions dropdown, and apply a percentage change to the regular price or sale price across all selected products.
The critical issue with this approach is that it modifies your products' actual prices rather than sitting on top of them as a temporary rule. When the promotion ends, you have to run another bulk edit to reverse the change, and if your pricing isn't perfectly consistent across the catalog going in, recovering the original values precisely can be genuinely complicated.
For anything beyond a permanent catalog-wide price adjustment, bulk price editing is the wrong tool for a time-limited promotion.
Discounting All Products With a Sitewide Coupon
If you create a percentage coupon with no product or category restrictions, it applies to every item in a customer's cart.
Creating one under WooCommerce → Coupons → Add Coupon, selecting Percentage Discount, and leaving the product restrictions empty gives you an effective all-products discount that lives as a coupon code.
This approach is clean and reversible, too. All you need to do is deactivate the coupon, and the sale is over, without you having to touch any product prices. For campaigns where you want to track redemptions or limit eligibility, it also has the advantage of code-based attribution.
Its main downside, like all coupon-based discounts, is that customers have to know the code and enter it. A sitewide sale that lives behind a coupon code is less visible and less automated than one that applies to every order by default.
Discounting All Products Automatically With Elevated Discount Rules
Elevated Discount Rules is the most efficient way to discount all products in WooCommerce without editing prices or requiring the customer to enter a coupon code.

When you create a simple discount and set the product scope to apply to all products, the rule fires automatically on every purchase as soon as it is saved.

Every product in your catalog is discounted without any individual price editing, and when you want the promotion to end, you simply deactivate the rule. The underlying product prices remain untouched throughout.
You can also exclude specific products from an all-products rule if certain items shouldn't participate in the promotion. This exclusion option is available in the same discount form and doesn't require creating a separate rule for each excluded item.

This means a true "all products except these X products" discount is a one-rule setup rather than a multi-rule workaround.
You can also add promotional messaging to product pages via the plugin's display settings, so that customers browsing during the promotion see the discount clearly communicated.

An analytics feature that tracks rule performance over time is provided, which is useful for evaluating how an all-products promotion affected conversion and revenue.

Final Thoughts
Discounting all products in WooCommerce natively has several drawbacks. It is either too slow if you try to manually add the sale price, too risky if you try to bulk edit prices, or too limited in reach if you decide to go the sitewide coupon code route.
Elevated Discount Rules offers the cleanest approach: an all-products discount rule that applies automatically, keeps your catalog prices intact, and is as easy to end as it was to start.
For more options for managing WooCommerce discounts at scale, see our roundup of the 6 Best WooCommerce Discount Plugins.

