Short answer. Only after, not before. Article 1557 of the Civil Code says the warranty against eviction cannot be enforced until a final judgment has been rendered, by which you, as buyer, actually lose the thing acquired or part of it. You cannot invoke the warranty while the eviction case is still pending.
What the law says
The warranty cannot be enforced until a final judgment has been rendered, whereby the vendee loses the thing acquired or a part thereof.
Civil Code, Article 1557 — Warranty Requires Final Judgment. Read the full provision →
Why a final judgment is required first
Article 1557 sets a clear precondition: the warranty cannot be enforced until a final judgment has been rendered, whereby the vendee loses the thing acquired or a part thereof. This means the warranty against eviction is not something you can invoke the moment someone merely threatens or files a claim against your ownership; the law requires that the dispute over your title actually be resolved, and resolved against you, before the seller's warranty obligation is triggered.
What final judgment means for enforcing the warranty
Because the article specifically requires a final judgment, an ongoing case where the outcome is still uncertain, or a judgment that is still subject to appeal, does not yet satisfy this requirement. Only once the judgment has become final, resulting in you actually losing the thing acquired, or a part of it, does the warranty against eviction become enforceable against the seller. This ties the seller's liability to an actual, confirmed loss rather than a mere risk of one.
Why the law waits for the loss to actually happen
This requirement makes sense given what the warranty against eviction is meant to address: it protects you against genuinely losing the property to someone with a better right, not against every claim anyone might raise. Requiring a final judgment before the warranty can be enforced avoids the seller being held liable over disputes that might still be resolved in the buyer's favor, or that might never result in an actual loss of the property at all.
What this means for you while the case is still pending
While your eviction case is still being litigated, Article 1557 means you generally cannot yet enforce the warranty against your seller for that eviction; you have to wait until there is a final judgment against you before that specific remedy becomes available. This does not necessarily mean you have no other options in the meantime, since other rules can govern notifying your seller of the pending case, but this article specifically addresses when the eviction warranty itself becomes enforceable.
What to do before the judgment becomes final
Even though the warranty itself cannot yet be enforced, the time before final judgment is not simply a waiting period with nothing to do. Rules elsewhere in the Civil Code deal with a buyer's obligation to bring the seller into the eviction case, so the seller has notice and an opportunity to defend the title being challenged. Attending to that step matters precisely because Article 1557 ties the seller's liability to an outcome that has not yet occurred, so how the underlying case is handled while it is pending can affect the warranty claim once judgment finally becomes final.