16/04/2026
When Does a Contract Legally Form Under Thai Law? Key Principles and Supreme Court Guidance
Under Thai law, a contract is a juristic act formed by the mutual expression of intention of at least two parties. One party makes an offer and the other gives an acceptance. A legally binding contract arises when the offer and acceptance correspond in all essential respects. This fundamental principle is codified in the Civil and Commercial Code and has been consistently affirmed by the Supreme Court.
A critical starting point is the legal nature of an offer. An offer must contain clear and definite essential terms sufficient to give rise to a contract upon acceptance. If the statement lacks certainty, it may constitute merely an invitation to treat rather than a legally binding offer. In Supreme Court Decision No. 748/2544, a promotional brochure containing details such as property size, price, and payment terms was held not to be a valid offer but merely an invitation for interested parties to submit offers. Consequently, no contract arose in the absence of a proper offer and acceptance.
Where an offer specifies a period for acceptance, the offeror is bound by that timeframe and cannot revoke the offer during the stated period. This principle is reflected in Section 354 of the Civil and Commercial Code. In Supreme Court Decision No. 19-21/2537, the defendants issued an offer to sell land with a validity period of 180 days and undertook not to sell to any third party during that period. When the plaintiff accepted within the stipulated timeframe, the Court held that a binding contract had been formed. The defendants’ subsequent refusal to transfer the land constituted a breach of contract.
In cases where no timeframe for acceptance is specified, the law distinguishes between parties who are present and those at a distance. For parties at a distance, Section 355 provides that the offer cannot be revoked within a reasonable period during which acceptance may be expected. What constitutes a reasonable period depends on the circumstances, including the method of communication and the distance between the parties. For parties dealing face-to-face, including by telephone, Section 356 requires acceptance to be made immediately; otherwise, the offer lapses.
The lapse of an offer is further governed by Section 357, which provides that an offer ceases to be binding if it is rejected or if acceptance is not made within the applicable timeframe. This principle was illustrated in Supreme Court Decision No. 3801/2555, where a lease clause referring to future adjustment of rent or lease terms without specifying essential details was held to lack sufficient certainty. The absence of a valid acceptance meant that no binding contract was formed.
The legal effect of an acceptance must also be carefully considered. Under Section 359, an acceptance that introduces additional terms, limitations, or modifications is not a valid acceptance but is deemed a rejection and constitutes a new offer. Accordingly, a contract arises only when the acceptance mirrors the offer without variation.
In transactions between parties at a distance, Section 361 provides that a contract is formed at the moment the acceptance reaches the offeror. The term “reaches” refers to the point at which the acceptance enters the sphere of control of the offeror such that, in the ordinary course of events, the offeror would have knowledge of it. Importantly, the formation of the contract does not depend on payment or performance; once offer and acceptance coincide, the contract is complete. As a result, any subsequent payment may not qualify as a deposit if it is not made contemporaneously with contract formation.
Even where parties appear to agree, a contract may still not arise if essential terms remain unsettled or if the parties intend to formalize their agreement in writing. Section 366 addresses such situations. Where any term is expressly regarded by either party as essential and agreement has not been reached on that term, the law presumes that no contract exists. This was affirmed in Supreme Court Decision No. 3942/2545, where a reservation agreement for the purchase of property lacked agreement on key terms such as construction completion and transfer conditions. The Court held that no binding contract had been formed and ordered the return of the money as unjust enrichment.
Similarly, where the parties agree that a contract must be made in writing, Section 366 provides that no binding contract arises until the written agreement is executed. In Supreme Court Decision No. 2224/2553, a receipt acknowledging payment of a deposit and referring to a future written sale agreement was held insufficient to create a binding contract. The Court ruled that, in the absence of the written agreement, the contract had not come into existence and the deposit had to be returned.
In conclusion, the formation of a contract under Thai law depends not on formality but on the precise alignment of offer and acceptance, the certainty of essential terms, and compliance with statutory requirements governing timing and communication. Misunderstanding these principles may result in unintended legal consequences, including unenforceable agreements or liability for restitution. Expat Juris regularly advises clients on structuring contracts to ensure clarity, enforceability, and full legal protection under Thai law.
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