Join us in bringing joy to customer experience. Five9 is a leading provider of cloud contact center software, bringing the power of cloud innovation to customers worldwide.

Living our values everyday results in our team-first culture and enables us to innovate, grow, and thrive while enjoying the journey together. We celebrate diversity and foster an inclusive environment, empowering our employees to be their authentic selves.

About the Role

We are looking for a Senior .NET Developer who combines deep technical expertise with a passion for code quality, mentorship, and collaborative delivery. In this role you will lead efforts to modernize and evolve our platform, drive engineering best practices, and work alongside product, design, and data teams to ship reliable software at scale.

You bring a proven track record in .NET development, a sharp understanding of modern deployment pipelines, and the architectural awareness to build systems that scale across tenancy models and data workloads.

Core Responsibilities

Technical Leadership & Code Modernization

• Lead architectural decisions for migrating a legacy single tenant .NET 8 application into an existing multitenant framework.
• Champion clean code principles and drive technical roadmaps that reduce technical debt while maintaining delivery velocity.
• Evaluate and introduce tooling, libraries, and frameworks that improve developer experience and system reliability.
• Mentor junior and mid-level engineers through pairing, design reviews, and structured knowledge-sharing sessions.

Code Review & Quality Assurance

• Conduct constructive code reviews that uphold team standards and serve as teaching opportunities.
• Define and enforce coding standards, naming conventions, and architectural guidelines across the team.
• Identify systemic quality issues through review patterns and proactively propose process improvements.
• Act as a trusted technical reviewer for high-risk or cross-cutting changes before they reach production.

Cross-Functional Collaboration

• Partner closely with stakeholders to translate business requirements into accurate technical estimates and clear implementation plans.
• Collaborate with data engineers on warehouse integrations and backend data pipelines, ensuring scalable and maintainable interfaces.
• Work with DevOps and platform teams to define deployment patterns and promote infrastructure-as-code practices.
• Facilitate cross-team alignment through clear written communication, architectural decision records (ADRs), and documentation.

Quality Engineering & Testing with TDD

• Apply test-driven development (TDD) as a core engineering discipline, writing unit, integration, and contract tests before implementation.
• Design and maintain test suites that give the team confidence to refactor and deploy frequently.
• Champion a shift-left testing culture by embedding quality practices into every stage of development, not just QA cycles.
• Ensure test coverage benchmarks are defined, tracked, and continuously improved.

Communication & Process Leadership

• Lead sprint ceremonies including planning, retrospectives, and backlog grooming with clarity and accountability.
• Produce high-quality technical documentation including runbooks, API contracts, and onboarding guides.
• Surface blockers and dependencies early, communicating status and risk proactively to stakeholders.
• Contribute to a culture of psychological safety where candid, constructive feedback is the norm.

Required Qualifications

• 5+ years of professional software development experience with a focus on .NET.
• .NET proficiency, including ASP.NET Core, Entity Framework Core, and the modern .NET runtime ecosystem.
• Demonstrated experience modernizing legacy web applications — refactoring, re-architecting, or re-platforming from older monolithic web applications to modern platform fabrics.
• Solid understanding of CI/CD pipelines, including pipeline design, automated test gating, artifact management, and deployment strategies (blue/green, canary, rolling).
• Clear understanding of single-tenancy vs. multi-tenancy architecture patterns and the trade-offs in security, isolation, scalability, and cost.
• Experience with test-driven development and a strong testing philosophy covering unit, integration, and end-to-end coverage.
• Strong written and verbal communication skills; able to write clear technical documentation and lead design discussions.

Preferred Qualifications

• Claude code, Copilot, or the leverage of any AI platform to increase production output is a strong plus.
• Experience with large-scale data warehousing solutions; Google BigQuery experience is a strong plus.
• Frontend experience with Vue.js 3 — component architecture, Composition API, and state management patterns.
• Familiarity with observability tooling such as OpenTelemetry, Prometheus, Datadog, or similar.
• Experience working in a platform or multi-product engineering environment.

Benefits:

• Five9 Shares
• Bonus Scheme
• 10% Flexi Benefit
• Meal Allowance
• Medical Insurance
• Life Insurance
• 25 day Annual Leave + Public Holidays

Five9 embraces diversity and is committed to building a team that represents a variety of backgrounds, perspectives, and skills. The more inclusive we are, the better we are. Five9 is an equal opportunity employer.

View our privacy policy, including our privacy notice to California residents here: https://www.five9.com/pt-pt/legal.

Note: Five9 will never request that an applicant send money as a prerequisite for commencing employment with Five9.