Short answer. No, generally not. Article 1439 limits estoppel to the parties involved or their successors in interest. A stranger to the original transaction cannot invoke it to claim a benefit, and cannot be bound by it either, because estoppel is personal to those whose conduct created it.
What the law says
Estoppel is effective only as between the parties thereto or their successors in interest.
Civil Code, Article 1439 — Estoppel Binds Only the Parties and Their Successors. Read the full provision →
Estoppel is personal to the parties
Article 1439 states the rule directly: estoppel is effective only as between the parties thereto or their successors in interest. Estoppel arises because one party's own words, conduct, or silence induced another to rely on a certain state of facts. That reliance is what the law protects, and only the person who relied — or the party whose conduct created the reliance — is bound by the result. A person who had no part in that exchange, and did not rely on anything the other side said or did, has no claim to invoke it.
Who counts as a 'successor in interest'
The article extends the same effect to successors in interest of the original parties. This covers someone who steps into a party's shoes after the estoppel arose — an heir, an assignee, or a buyer of the party's rights — because that person's claim derives from, and is no better than, the party they succeeded. A true outsider is different: someone who was never a party and never derived their rights through one cannot use, or be tied down by, an estoppel that arose entirely between other people.
Why a third person cannot rely on it
The rationale is that estoppel is not a general rule of law available to anyone who finds it convenient — it is a consequence tailored to a specific relationship where one side's representation caused the other's reliance. A stranger who was never told anything and never changed position in reliance on it has nothing to point to that would justify the same protection. Letting outsiders invoke estoppel they had no part in would stretch the doctrine well past what actually justifies binding someone to a representation.
The practical takeaway
If you were not a party to the transaction or conduct that created the estoppel, and you did not acquire your rights from someone who was, Article 1439 means you generally cannot use that estoppel either as a shield or a sword. Your position has to be evaluated on its own footing — whatever rights or defenses you actually have, independent of what was said or done between the two original parties. Whether some other doctrine applies to your specific facts is a separate question this article does not answer.