Yes, one person can sign a contract for both parties, but only when that person holds formal authority to act on the other side’s behalf. That authority usually comes from a power of attorney, a corporate officer role, or another agency relationship that lets one individual bind someone else. Without it, a dual signature can leave the contract unenforceable against the party who never authorized it and expose the signer to personal liability.
Where the Authority to Sign for the Other Side Comes From
Signing for two parties is only lawful if you actually represent the second one. The source of that representation has to be something a court can point to.
Power of Attorney
A power of attorney is a legal document in which one person (the principal) grants another person (the agent, sometimes called an “attorney-in-fact”) the right to make binding decisions on their behalf. The document itself defines how broad or narrow that authority is. A general power of attorney might cover virtually any financial or legal transaction. A limited one might authorize the agent to sign a single real estate closing and nothing else. If the POA doesn’t cover the type of contract being signed, the agent has no authority to sign it, and the contract fails as to the principal.
Corporate Officers and LLC Managers
In the business world, specific people are authorized to sign contracts that bind the entire company. For a corporation, that authority usually belongs to officers like the CEO or president, though a company’s bylaws or a board resolution can extend signing authority to other officers or employees. Some companies limit the authority by dollar amount or transaction type. A vice president might be authorized to sign contracts up to a certain value, with anything above requiring the CEO’s signature.
For a limited liability company, signing authority depends on structure. In a member-managed LLC, any member can generally bind the company. In a manager-managed LLC, only designated managers hold that power. The operating agreement spells out who can sign what, and anyone dealing with an LLC should ask for the relevant provisions before relying on someone’s claimed authority.
This is what makes dual signing possible in the common business case: one person can legitimately be the authorized officer of Company A and the authorized manager of Company B, and sign a contract between them in both roles.
The Self-Dealing Problem
The hardest situation arises when the person signing for both parties has a personal stake in the transaction. If you’re an officer of Company A and also own Company B, and you sign a contract between the two, you’re on both sides of the deal. Courts call this self-dealing and treat it with heavy skepticism. When the same person controls both sides of a negotiation, there’s no one pushing back on price, terms, or fairness.
Fiduciary transactions where the parties aren’t negotiating at arm’s length can be set aside at the request of the disadvantaged party. The contract isn’t automatically void, but it is voidable, meaning the harmed party can ask a court to undo it.1Federal Deposit Insurance Corporation. Section 8 Trust Manual – Compliance/Conflicts of Interest, Self-Dealing and Contingent Liabilities The burden of proof also flips. Instead of the complaining party having to show the deal was unfair, the self-dealing party must prove the transaction was entirely fair and that the conflict was fully disclosed to everyone involved. Failing to carry that burden means the contract gets unwound regardless of whether the terms were actually reasonable.
The practical response: if you’re signing for both sides, get independent review. Approval by the board of directors, an independent committee, or outside counsel goes a long way toward showing that the deal was fair. Complete documentation of the decision-making process matters enormously if the contract is ever challenged.1Federal Deposit Insurance Corporation. Section 8 Trust Manual – Compliance/Conflicts of Interest, Self-Dealing and Contingent Liabilities
How to Format the Signature Block
When one person legitimately signs for both parties, the signature block needs to make the arrangement unmistakable. Ambiguity here creates real risk. If it’s unclear in what capacity someone signed, they might be treated as personally liable, or the contract might not bind the party they intended to represent.
If you’re signing for yourself and also for another individual under a power of attorney, use two separate signature lines. Your own line is straightforward. The second should read something like: “John Smith, by Jane Doe as Attorney-in-Fact.” That format identifies the principal, the agent, and the source of authority.
If you’re an officer of two companies entering a contract with each other, each company gets its own signature block. The first: “Company A, Inc., by John Smith, President.” The second: “Company B, LLC, by John Smith, Manager.” The title matters. Signing as “President” for one entity and “Manager” for the other shows you’re acting in a specific corporate role each time, not in your personal capacity.
Attach the authorizing document whenever possible. If you’re signing under a POA, append a copy to the contract. If your authority comes from a board resolution or operating agreement provision, include that too. Anyone reviewing the contract later, whether a court, an auditor, or a successor in interest, can then verify the signer’s authority without tracking down separate documents.
Signing Electronically for Both Sides
Federal law treats electronic signatures the same as handwritten ones. Under the Electronic Signatures in Global and National Commerce Act, a signature or contract cannot be denied legal effect solely because it is in electronic form.2Office of the Law Revision Counsel. United States Code Title 15 Section 7001 – General Rule of Validity The same rules about authority, capacity, and proper documentation apply whether you’re signing with a pen or through an e-signature platform.
The mechanics are actually easier to get right electronically. Most e-signature platforms let you set up multiple signature fields with distinct labels, so you can execute each block separately in its designated capacity. The audit trail records the timestamp and identity verification for each signature event, which strengthens the evidentiary record. Label each signature with the signer’s capacity, and upload the authorizing document as an attachment within the signing package.
What Happens If the Signer Lacks Authority
If someone signs another person’s name on a contract without permission, the person whose name was used is generally not bound. An unauthorized signature is ineffective against the principal. The agreement simply doesn’t create obligations for someone who never authorized it, and the other contracting party is left with a deal that may be unenforceable against the very person they thought they were contracting with.
The unauthorized signer doesn’t walk away clean, though. Someone who signs a contract claiming to represent another person, when they actually have no authority to do so, can be held personally liable to the third party. By signing, the person implicitly guaranteed they had authority. When that guarantee turns out to be false, the third party’s losses fall on the person who made the false representation.
An unauthorized signature isn’t always fatal. If the principal later learns about the contract and decides to adopt it, they can ratify the agreement. Ratification is the act of approving an unauthorized act after the fact, and it makes the contract enforceable as if the signer had proper authority all along. It can happen explicitly, through a written approval, or through conduct, such as knowingly accepting the benefits of the deal. Ratification has to cover the entire transaction; a principal can’t cherry-pick favorable terms and reject the rest. And it must happen while ratification is still possible. If the third party has already withdrawn or circumstances have fundamentally changed, it may be too late.
At the far end of the spectrum, signing someone else’s name without any authorization and with intent to deceive is forgery. Forgery is a criminal offense in every U.S. state and can apply to contracts, checks, wills, and other legal documents. An honest mistake about the scope of one’s authority is a civil problem. Deliberately faking a signature to commit fraud is a criminal one.