Principal Machine Learning Engineer

Harnham; Barcelona; Hybrid; EUR 81,000 - 135,000; Full time

Benefits offered by this job

Salary up to €135,000

Job summary

Harnham is seeking a Principal Machine Learning Engineer for a high-growth AdTech scale-up with ML at the heart of the product. You will report to the CTO, shape technical strategy, and lead cross-team ML initiatives while staying hands-on in model development that powers real-time bidding and attribution.

You will guide ML direction, design production systems, mentor engineers and drive MLOps and observability, aligning technical work with commercial goals across global teams.

Qualifications

• Senior, Staff or Principal ML Engineer with production experience.
• Proven track record deploying ML systems at scale.
• Experience in AdTech, programmatic advertising or DSP is highly desirable.
• Strong Python and ML engineering skills; PyTorch or TensorFlow proficiency.

Responsibilities

• Define technical direction and influence ML strategy across teams.
• Design, build and deploy ML models in production environments.
• Develop recommendation, bidding, attribution and churn models.
• Scale ML infrastructure, experimentation platforms and training pipelines.
• Mentor engineers and contribute to architecture decisions.

Skills

Machine Learning Engineer

Python

MLOps

Tools

PyTorch

TensorFlow

Job description

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