Paris or Barcelona (2 days a week in office)
This is an opportunity to join a high-growth technology business where machine learning sits at the heart of the product.
Reporting directly to the CTO, you will influence technical strategy, lead complex machine learning initiatives, and remain hands-on with the development of models that power large-scale commercial decision-making.
THE COMPANY
They are a profitable AdTech scale-up specialising in AI-driven performance advertising.
Their platform helps businesses acquire and re-engage users through highly targeted digital advertising, using machine learning to determine which users see specific adverts and when.
Having achieved significant growth in recent years, they continue to invest heavily in their machine learning and data capabilities while maintaining a collaborative, engineering-led culture.
Their teams are distributed internationally and work on products that make billions of real-time decisions each day.
THE ROLE
As a Principal Machine Learning Engineer, you will combine technical leadership with hands-on machine learning engineering responsibilities.
Specifically, you can expect to be involved in the following:
Defining technical direction and influencing machine learning strategy across multiple teams
Designing, building and deploying machine learning models in production environments
Developing recommendation systems and bidding algorithms within a large-scale advertising ecosystem
Building audience targeting and mobile attribution models
Creating customer lifetime value and churn prediction models
Scaling machine learning infrastructure, experimentation frameworks and training pipelines




Driving best practices across MLOps, model monitoring, observability and automated retraining
Partnering with engineering leadership and business stakeholders to align technical solutions with commercial objectives
Mentoring engineers and contributing to architecture and platform decisions across the machine learning function
Leading the development of new machine learning capabilities from research through to production deployment
SKILLS AND EXPERIENCE
The successful Principal Machine Learning Engineer will have the following skills and experience:
Strong commercial experience as a Machine Learning Engineer at Senior, Staff or Principal level
Proven track record of building and deploying production machine learning systems at scale
Experience within AdTech, programmatic advertising, RTB or DSP environments is highly desirable
Expertise in one or more of the following areas: recommendation systems, audience targeting, attribution modelling, customer lifetime value modelling or churn prediction
Strong Python and machine learning engineering skills
Experience with modern machine learning frameworks such as PyTorch, TensorFlow or similar technologies
Exposure to MLOps tooling, experimentation platforms and large-scale data environmentsExperience leading technical initiatives and influencing engineering direction
Ability to communicate complex technical concepts to both technical and non-technical stakeholders
PhD or advanced academic background in a STEM discipline is beneficial but not essential
BENEFITS
The successful Principal Machine Learning Engineer will receive the following benefits:
Salary up to €135,000 - depending on experience
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📌 Principal Machine Learning Engineer (Barcelona)
🏢 Harnham
📍 Barcelona