Senior Full Stack Engineer Jobs in Markham, ON (NOW HIRING)

Are you a highly experienced full-stack engineer who thrives on solving complex technical challenges and delivering production-ready solutions at speed? We are seeking a Senior Staff Full-Stack Engineer – .NET, React & AI to play a key role in building an AI-driven engineering platform where innovation, ownership, and technical excellence are at the heart of everything.

The successful candidate will be responsible for designing, building, and delivering product features end-to-end while helping shape a highly scalable, AI-centric platform that powers multiple brands from a shared technology foundation.

As a Senior Staff Full-Stack Engineer – .NET, React & AI, you will take ownership of product delivery from concept through to production. You'll work across the full technology stack, leveraging AI coding agents and modern engineering practices to accelerate delivery without compromising quality. This role combines hands-on software development, technical leadership, systems architecture, and platform engineering in a fast-paced environment where autonomy and accountability are highly valued.

• Own the end-to-end delivery of product features, including design, development, testing, verification against acceptance criteria, and production deployment.
• Build and maintain third-party and B2B integrations, delivering customer- and brand-specific functionality on top of a shared, scalable platform.
• Leverage AI coding agents and automated verification tools to improve development speed while maintaining engineering quality standards.
• Design, build, and operate highly available, high-performance distributed systems.
• Establish technical patterns, mentor through example, and remove technical roadblocks across multiple concurrent workstreams.
• Monitor production environments, investigate issues, and continuously improve platform reliability, observability, and deployment processes.

• Extensive commercial experience delivering production-grade, full-stack applications.
• Strong expertise in .NET / C#, RESTful API development, and Next.js / React, including server-side rendering and real-time streaming using Server-Sent Events (SSE).
• Proven experience designing and operating highly available, high-throughput systems at scale.
• Hands-on experience with MongoDB, PostgreSQL, and Redis, with the ability to select the appropriate data store based on workload.
• Experience building event-driven architectures using Apache Kafka or similar event hub technologies, including producer/consumer patterns, schema design, and real-time data processing.
• Demonstrated experience designing and delivering third-party and B2B API integrations.
• Strong understanding of API security, including OAuth authentication, HMAC request signing, idempotency, replay protection, and audit logging.
• Practical experience using AI-assisted development tools and coding agents to improve engineering productivity.
• Experience with production monitoring, observability, CI/CD pipelines, and issue triage using tools such as Sentry or equivalent.

• Proven ability to deliver high-quality software within demanding timelines while balancing speed and quality.
• Comfortable managing multiple priorities across concurrent workstreams.
• Demonstrated ownership of projects from ambiguous requirements through to successful production delivery.
• A proactive, solutions-focused mindset with the confidence to make informed decisions, navigate uncertainty, and independently drive outcomes.

• Exposure to cutting-edge AI and automation technologies that are reshaping modern engineering and business operations.
• The opportunity to work on genuinely challenging projects using modern tools and technologies.
• A collaborative, high-performing environment where innovation, accountability, and technical excellence are recognized and rewarded.
• Clear opportunities for professional growth and career progression as the organization continues to scale.
• Competitive salary with a discretionary bonus.
• Comprehensive health benefits, including extended healthcare, dental, and vision coverage.
• On-site leisure facilities to help you recharge throughout the day.
• Regular company events that celebrate success and foster team connection.
• On-site parking for added convenience.

If you're an engineer who enjoys taking ownership, solving complex problems, embracing emerging AI technologies, and building systems that operate at scale, this is an opportunity to make a meaningful impact while working alongside talented professionals who value innovation, collaboration, and continuous improvement.