Senior Software Engineer - Biometrics

At Fourthline, our mission is to fight financial crime. We help protect the global financial system by verifying millions of identities for banks, neobanks, online brokers, crypto exchanges, and insurers like N26, Trade Republic, flatexDEGIRO, Nationale Nederlanden, Qonto, Shine, Solarisbank, and more.

Having started our journey in January 2018, we're incredibly proud to count around 250 employees between our Amsterdam and Barcelona offices with over 50 nationalities.

Your Mission at Fourthline

Prevent financial crime by building best-in-class software alongside a talented and driven team, shaping our Biometrics solution at the core of Identity Verification, ensuring accuracy, scalability, and fraud prevention. You will work on complex, scalable, performant, data-intensive systems for facial recognition and liveness detection, and work closely with AI/ML engineers to integrate the latest models into production-grade services.

This role would be part of our Biometrics team, lead by Aytul Saka. Our Biometrics team builds and maintains backend systems that power identity verification through biometric technologies, and collaborates closely with AI/ML engineers to integrate cutting-edge models into production-grade services. Our core capabilities include face search, liveness detection, and deepfake detection, which are used as checks during the identity verification process. These services analyze user-provided data to ensure that a real, present person is being verified and to detect potential fraud or spoofing attempts. 

As a Senior Backend Engineer at Fourthline, you will:

• Design, develop, maintain, and improve our microservices, taking responsibility for thorough testing and reliable deployments.


• Manage your tasks, priorities, and deliverables, taking joint ownership with your teammates for sprint goals.


• Use your experience to contribute to our growth through lessons learned from your successes and failures.


• Take responsibility for engineering excellence and participate in architectural decision-making within your team.


• Contribute to thorough documentation to ensure clarity and long-term maintainability.


• Understand the entire development lifecycle and work closely with other members in squads, including Platform and QA teams.


• Apply both technical and interpersonal skills to solve challenges, recognizing that the best solutions often combine technology with people.

Collaboration

At Fourthline, we foster a collaborative culture informed by deep FinTech knowledge and a strong understanding of our business objectives. You will actively participate in chapter meetings, knowledge-sharing sessions, and cross-discipline collaboration with other teams and engineering disciplines.

Career Growth and Development

At Fourthline, we offer clear opportunities for learning and development, allowing you to work alongside and learn from experienced engineers. As you grow within our team, there are opportunities to grow your impact toward Staff Engineer level and beyond, including:

• Deepening your technical expertise


• Expanding your influence across teams


• Strengthening your problem-solving and communication skills


• Building your knowledge of the FinTech industry

Our Stack

.NET 8–10 — Our cloud-based microservices architecture includes REST APIs, Docker, Kubernetes, Message Queues (RabbitMQ), RDBMS (PostgreSQL), Wolverine, Marten (Doc + Event stores), and more.

What You Bring

Required

• 5+ years of professional software development experience, with strong expertise in .NET and C#


• Deep knowledge of .NET 8–10 and experience building and operating production-grade systems


• Proven experience designing, building, and maintaining microservices architectures


• Strong understanding of RESTful API design and distributed systems


• Experience with asynchronous and event-driven architectures (e.g. messaging systems like RabbitMQ)


• Solid understanding of software design principles (SOLID), design patterns, and Domain-Driven Design (DDD)


• Experience with relational databases (e.g. PostgreSQL) and ORMs such as Entity Framework Core


• Strong testing practices, including unit and integration testing


• Experience with cloud platforms (AWS and/or Azure) and containerization (Docker, Kubernetes)


• Experience with CI/CD pipelines and modern DevOps practices


• Ability to make architectural decisions and drive technical discussions


• Strong ownership mindset and ability to lead complex initiatives end-to-end


• Product mindset with the ability to drive successful business outcomes, making pragmatic trade-offs aligned with product goals


• Effective communication skills and ability to collaborate across teams


• Full professional proficiency in English


• Ability to work from our Amsterdam office 3 days a week

Nice to Have

• Experience with Wolverine and/or Marten


• Familiarity with biometrics or computer vision systems


• Experience working in a regulated FinTech or financial services environment

What We Offer

• Competitive salary 


• Career progression opportunities toward Staff Engineer and beyond


• A collaborative, cross-functional engineering culture


• Learning and development opportunities


• Hybrid working from our Amsterdam office

At Fourthline, we believe diversity enriches our culture and inspires you to do your best work. We value your unique talents and perspectives, welcoming them into a safe and inclusive working environment, to ultimately deliver the best products to our customers and society. You're welcome here. Fourthline is for everyone.

Our hiring process is designed to be equal, fair, and transparent. We welcome people from all backgrounds, ethnicities, genders, sexual orientations, ages, abilities, religions, and experiences in life. If you're excited about this role, but your experience does not align perfectly with every qualification in the job description, we encourage you to apply anyways. You may just be the right candidate for this or other roles.