Short answer. Yes. A guaranty can still be entered into even without the principal debtor's knowledge or consent, or even against the debtor's will. The law does not treat the debtor's participation as required for the guaranty itself, though separate provisions then govern what the guarantor can later recover from the debtor.
What the law says
If a guaranty is entered into without the knowledge or consent, or against the will of the principal debtor, the provisions of articles 1236 and 1237 shall apply.
Civil Code, Article 2050 — Guaranty Without the Debtor's Knowledge. Read the full provision →
The guaranty does not need your involvement to exist
A guaranty is fundamentally an agreement between the guarantor and your creditor — it promises the creditor that if you fail to pay, the guarantor will. This article confirms that arrangement can go forward "without the knowledge or consent, or against the will of the principal debtor," meaning you. You are the debtor being guaranteed, not necessarily a party the law requires to sign off before the guaranty takes effect between the guarantor and the creditor.
The real question shifts to what happens between you and the guarantor
Once a guaranty like this exists, the article does not leave the relationship between you and the guarantor unaddressed — it points squarely to "the provisions of articles 1236 and 1237" to govern it. Those are the Civil Code's general rules on what a person who pays a debt on someone else's behalf can and cannot later recover from that debtor, and they apply with particular force where the debtor never knew about, or actively opposed, the arrangement.
Why the distinction between validity and recovery matters to you
If you discover a guaranty was arranged behind your back, the instinct is to ask whether it counts at all. This article answers that narrow question — yes, it can be valid as between the guarantor and the creditor. But that is a separate question from how much the guarantor can eventually collect back from you if they end up paying on your behalf, and how far your obligation to reimburse them extends. That second question is governed by Articles 1236 and 1237, not by this article.
What this means practically if you find yourself in this situation
If you learn that someone guaranteed your loan without asking you, do not assume either that the guaranty is worthless because you never agreed to it, or that you automatically owe the guarantor the full amount they might pay. Both assumptions skip past what the statute actually does: it validates the guaranty as an arrangement between guarantor and creditor, then routes your exposure through separate rules that specifically account for the fact that you were not consulted or did not consent.