Yes. Pick the Both card under You are joining as when you register, and one account unlocks the buyer side and the supplier side together.
Your dashboard then shows both sides at once: on the buyer side the New Demand and My Demands shortcuts plus your demand counts, on the supplier side the Marketplace shortcut with Offers submitted and Win rate. The monthly demand and weekly offer meters sit next to each other, so you never need two separate accounts. The navigation lists both the Buyer and Supplier areas.
On the subscription side, Choose your plan offers three families: Buyer, Seller and Suite. Suite bundles the buyer and seller subscription into one subscription and one invoice — that is the family for companies doing both. You can switch between families and change tier at any time: an upgrade applies immediately, a downgrade at the start of the next period.
Your role is shown under Settings → My Account.
Also asked as: Can I open demands and submit offers from the same account? · Do I need two separate accounts for buying and selling? · What does the Both role do? · Can buyer and seller subscriptions be billed on one invoice?