Lead Smart Contract Engineer

• This position is open to U.S.-based candidates only, applications from other regions will not be considered.

• Contract Duration: Initial 2–3 month contract with the potential for long-term extension or full-time conversion based on performance and company fit.
  

Our client — an early-stage fintech startup — is developing a blockchain-based payment system designed to enable real-time, 24/7 movement of digital money across traditional finance and digital asset ecosystems. The company is building a new class of financial infrastructure that brings cash on chain through tokenization, powering payments for banks, digital asset exchanges, and the customers they serve.

We’re seeking a Lead Smart Contract Engineer to architect and implement secure, scalable smart contracts within a ZK Sync–based environment. You’ll help design and build the on-chain infrastructure that powers real-time tokenized payments and settlements — a critical foundation for next-generation financial systems.

Reporting directly to the CTO, you’ll be responsible for the end-to-end design, development, and security of smart contract systems. This includes building core payment and settlement contracts, establishing best practices for testing and deployment, and collaborating with internal teams and external stakeholders to bridge on-chain infrastructure with traditional finance systems. This is a greenfield opportunity — you’ll be building everything from the ground up.

• Architect and implement smart contracts for payment protocols, tokenization, and settlement on ZK Sync

• Write production-ready Solidity code for core financial contracts, multi-signature wallets, and token standards

• Conduct formal verification, invariant testing, and advanced security reviews to ensure contract safety

• Use Foundry for testing, fuzzing, and deployment automation

• Build TypeScript/Node.js integration services connecting contracts with backend systems (via WebSockets/webhooks)

• Lead technical decision-making around gas optimization and ZK rollup implementation strategies

• Establish internal standards for documentation, testing, and deployment

• Collaborate with stakeholders to align compliance requirements with decentralized design principles

• 5+ years of experience in smart contract development using Solidity and the EVM

• Proven record deploying and managing production contracts exceeding $10M TVL

• Deep understanding of smart contract security, vulnerabilities, and mitigation strategies

• Hands-on experience with Foundry for testing, debugging, and CI/CD integration

• Strong knowledge of ZK rollups, especially ZK Sync architecture

• Experience building real-time systems (WebSockets, webhooks)

• Expertise in DeFi protocols and token standards (ERC-20, ERC-721, ERC-4626)

• Ability to work independently as the smart contract domain expert

• Familiarity with formal verification tools and smart contract audits