Mendix Modernization Legacy Application Developer

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About the Role

RELYzIT Talent is seeking a Mendix Modernization Legacy Application Developer for a transformative, high-impact freelance mission in Brussels, Belgium. You’ll join a multidisciplinary team to modernize a complex legacy application—over 150,000 lines of ColdFusion code—into a future-proof, low-code Mendix platform. This is a rare opportunity to shape the digital backbone of a major organization, leveraging AI-driven migration and model-driven development to deliver lasting value.

Why This Role Matters

Our client’s legacy application is critical to their operations, supporting file management, data processing, and reporting across 20+ modules. Modernizing this system is essential for agility, scalability, and future innovation. Your expertise will directly impact the efficiency, quality, and sustainability of this transformation—enabling the business to unlock new capabilities and reduce technical debt. Each project phase delivers standalone value, ensuring your work has immediate and lasting impact.

What You’ll Be Doing

• Analyze and understand complex legacy business logic and application structures.


• Design and implement innovative, automated migration strategies using AI, code analysis, and model-driven development.


• Develop, adapt, and extend Mendix components, including screens, microflows, and integrations.


• Collaborate with a multidisciplinary team to maximize reuse of existing assets and accelerate migration.


• Work out user stories into robust, scalable Mendix solutions.


• Perform unit testing and ensure high-quality deliverables at every project phase.


• Contribute to the vision note, demonstrating how your approach has succeeded in similar modernization projects.


• Engage in Agile/Scrum ceremonies, driving continuous improvement and rapid iteration.


• Document and validate all required certificates and project evidence for compliance and transparency.

What We’re Looking For

• Builder mindset: You take ownership, thrive on solving complex problems, and deliver measurable impact.


• Proven experience in Mendix development, with at least Mendix Advanced Developer certification or equivalent expertise.


• Hands-on experience with AI-assisted development and automated code migration methodologies.


• Strong background in modernizing large-scale, legacy business applications.


• Ability to analyze, value, and reuse existing source code and business logic for efficient migration.


• Demonstrated success applying innovative migration solutions in real-world projects.


• Excellent communication skills and a collaborative, multidisciplinary approach.


• Meticulous about documentation and validation of all required certificates and project evidence.


• Fluent in English; knowledge of French or Dutch is a plus.


• Partial remote work possible; on-site presence in Brussels as required by project phase.

Technical Skills & Requirements

• Mendix Development (Expert level)


• Mendix Intermediate Advanced Developer certification or higher


• AI-assisted development and code analysis tools


• Experience with complex business processes and large-scale application modernization


• Agile/Scrum methodologies (Confirmed)


• Unit testing and quality assurance in Mendix environments


• Model-driven development and automated migration frameworks


• Ability to provide and validate all required certificates and supporting documents

Language Proficiency

• Fluent English required


• French or Dutch proficiency is an advantage

Other Requirements

• Freelance position with a project duration of up to 25 months


• Partial remote work; on-site in Brussels as needed


• All certificates and supporting documents must be attached to your CV for validation


• Assignment is time & material; possible extension if project duration exceeds initial estimate


• Each project phase is ordered separately and delivers standalone value


• Profiles must have demonstrable access to and knowledge of the proposed modernization solutions

Join the RELYzIT Talent Community

This is your chance to build the future—where your expertise shapes mission-critical systems and your VECTOR7™ credential sets you apart for life. If you’re ready to lead, innovate, and deliver at the highest level, we want to hear from you.