The increasing use of electronic documents and remote online offices in this digital era raises concerns about the security of electronic transactions, especially with the emerging quantum computing that threatens current encryption methods. Actually, quantum computers pose significant risks to current cryptographic systems, particularly those based on public-key cryptography. Quantum algorithms can speed up brute-force attacks on cryptographic algorithms and reduce the time required to search through the keyspace, posing a potential risk to the current encryption schemes and digital signatures. In addition, the existing electronic signature platforms have the problem of data-centred management, which makes them vulnerable to many security issues including data loss, tampering, leakage and other forms of cyberattacks. This paper presents an innovative solution to solve these problems by proposing “QuantumSing”, a novel distributed e-signature system based on post-quantum cryptography and blockchain technology. QuantumSing uses the FALCON algorithm to create secure post-quantum signatures that are resistant to quantum-based attacks and blockchain to ensure the integrity of the electronic contract and the non-repudiation of the electronic signatures. Furthermore, QuantumSing has a user-friendly and intuitive web service that enables users to sign and verify their electronic documents in a simple, efficient, and secure manner.