Senior Full Stack Developer Jobs in Milton, ON (NOW HIRING)

We are seeking a Senior Full Stack Engineer to help build and scale Mattermost's core web platform for teams operating in defense and critical infrastructure sectors. You will contribute across our Go backend and React/TypeScript web frontend, building features that hold up under strict security, compliance, and reliability requirements.

Our engineering culture is AI-forward. We expect engineers to work fluently with AI coding agents such as Claude Code day-to-day - for scaffolding, refactors, code review, and test generation - and treat that as core craft rather than a shortcut. We would rather hire smart people who get stuff done than chase an exact tech-stack match. If you have a track record of shipping and owning complex software end-to-end, we want to hear from you.

What You Will Do

• Architect and build full-stack features optimized for scalability and performance across Go, React, TypeScript, PostgreSQL, and Redis
• Leverage AI coding agents such as Claude Code and Cursor as a core part of your daily workflow while retaining full accountability for correctness, security, and design decisions
• Develop internal tooling and testing infrastructure to speed up the team's delivery, including agentic workflows and skills that make AI tooling more effective for the broader team
• Own testing strategy across frontend and backend code you ship
• Design and consume REST and WebSocket APIs with solid networking fundamentals
• Maintain the security and compliance standards required by our government and enterprise clients
• Contribute to Mattermost's open-source codebase

What We Are Looking For

Required:

• Strong full-stack development experience in Go and React, or a comparable stack
• Experience designing and consuming REST and WebSocket APIs with solid networking fundamentals
• Relational database experience including PostgreSQL, schema design, and query optimization
• Hands-on daily fluency directing AI coding agents such as Claude Code, Cursor, or Copilot for scaffolding, refactors, code review, and test generation - with the judgment to know when to trust the output and when to take the wheel yourself
• Bias toward shipping and owning complex software end-to-end without close supervision

Nice to Have:

• Experience with distributed systems or high-availability service architecture
• Familiarity with enterprise or regulated-environment security requirements
• Background in defense, intelligence, or critical infrastructure products
• Open-source contributions
• Experience working on distributed or remote-first teams
• Experience building tools, skills, or workflows on top of AI coding agents including MCP servers, agent skills, or CI-integrated agents

How Success Is Measured

• First 90 Days: Shipping full-stack features on the core platform using an AI-forward agentic development workflow and owning testing strategy across the code you ship.
• By Month 6: Internal tooling and testing infrastructure built that measurably speeds up the broader team's delivery. Agentic development practices adopted and contributing to team-wide velocity.
• At Year One: Recognized as the team's driver of agentic engineering practice. Deepening ownership of distributed systems and high-availability architecture. Contributing actively to Mattermost's open-source codebase.

Why Mattermost

• Mission-driven work: Your contributions directly support the organizations and missions that depend on secure, reliable collaboration including the U.S. Department of War and critical infrastructure operators worldwide
• Remote-first culture: Work from anywhere with a globally distributed, high-trust team built for autonomy and ownership
• AI-forward environment: We actively adopt and build AI-enabled workflows. Agentic development is core craft here, not a novelty
• End-to-end ownership: Ship and own complex software across the full stack with real accountability for what you build
• Open source at the core: Be part of a vibrant developer community shaping the future of secure collaboration

Compensation

Mattermost takes a market-based approach to pay. Actual compensation may vary based on location, skills, experience, qualifications, and market conditions.

Target Salary Range: CAD $132,591-$181,975

Canada Eligibility & Compliance

Candidates must be legally authorized to work in Canada without current or future sponsorship.

This role may require obtaining and maintaining a government security clearance or equivalent designation (such as Reliability Status or Secret clearance under Canada's Controlled Goods Program), depending on customer engagement. Candidates must meet eligibility requirements to be considered.

Given Mattermost's work with U.S. defense and government customers, some positions may also require compliance with U.S. export control laws, including EAR and ITAR, which can apply to non-U.S. based employees working on covered technical data. For more information, visit the Bureau of Industry and Security and the Directorate of Defense Trade Controls.