Principal Machine Learning Engineer

Harnham - Data and Analytics Recruitment; España; Hybrid; EUR 135,000 - 150,000; Full time

Job summary

Harnham - Data and Analytics Recruitment is seeking a Principal Machine Learning Engineer in Paris. You will define the technical direction of large-scale production ML systems while remaining hands-on across the full model lifecycle.

You will lead end-to-end ML initiatives across recommendations, audience targeting, and churn/LTV models, partnering with senior engineers and business stakeholders to translate commercial objectives into production-ready AI solutions.

Qualifications

• Experience building and deploying production ML systems at scale.
• Strong technical leadership with hands-on architecture direction.
• Experience with recommendation systems, audience targeting, LTV or churn models.
• Experience with MLOps, monitoring, retraining and deployment.

Responsibilities

• Define the technical direction of large-scale production ML systems and stay hands-on throughout the lifecycle.
• Lead end-to-end ML initiatives across recommender systems, audience targeting, and lifecycle modelling.
• Collaborate with senior engineers and business stakeholders to translate commercial objectives into production AI solutions.

Skills

Production ML systems

Technical leadership

Recommendation systems

Audience targeting models

LTV/churn models

MLOps platforms

Model monitoring

Automated retraining

Production deployment

Python

PyTorch

TensorFlow

Software engineering

Distributed systems

Stakeholder communication

AdTech/DSP experience

Education

PhD in STEM

Tools

PyTorch

TensorFlow

Job description

Principal Machine Learning Engineer

Location: Paris (Remote / Hybrid - Fully Remote or 2 Days in the Office)
Salary: 135,000 Base + 15,000 Bonus (OTE 150, 000)

THE COMPANY

This profitable French AdTech scale-up is transforming digital advertising through machine learning. By building AI-powered technology that determines which users are most likely to engage with an advert, they help leading mobile apps drive customer acquisition and re‑engagement through highly targeted advertising.

Following approximately 60% growth over the past two years, the business has expanded to around 140 employees across offices in Paris, Barcelona, Seoul and San Francisco, with more than 25 open positions supporting continued international growth.

You’ll be joining a highly technical engineering team, working directly alongside the CTO to shape the future of machine learning across the business.

THE ROLE

As a Principal Machine Learning Engineer, you'll define the technical direction of large-scale production machine learning systems while remaining hands‑on throughout the full model lifecycle. This is an individual contributor leadership role focused on delivering complex technical projects rather than managing people.

You'll lead end‑to‑end machine learning initiatives across recommendation systems, audience targeting, bidding optimisation and customer lifecycle modelling, partnering closely with senior engineering and business stakeholders to translate commercial objectives into production‑ready AI solutions. The role combines technical strategy, platform engineering and applied machine learning within a high‑scale real‑time environment.

YOUR SKILLS AND EXPERIENCE

• Extensive experience building and deploying production machine learning systems at scale
• Proven technical leadership, defining architecture and technical direction while remaining hands‑on
• Strong experience developing recommendation systems, audience targeting models, LTV or churn models
• Experience building robust MLOps platforms including model monitoring, automated retraining and production deployment
• Excellent Python and modern machine learning framework experience (PyTorch, TensorFlow or similar)
• Strong software engineering and distributed systems knowledge
• Ability to communicate complex technical concepts to senior stakeholders
• AdTech or Demand Side Platform (DSP) experience highly desirable
• PhD in a STEM discipline is advantageous

THE BENEFITS

• 135,000 base salary plus approximately 15,000 annual bonus (OTE 150, 000)
• Longevity bonus every two years
• 4.5-day working week with Friday afternoons off
• Fully remote working or hybrid (2 days per week if based near an office)
• Two company meet‑ups each year
• Work directly alongside the CTO
• Join a profitable, high‑growth international AI business with significant technical ownership opportunities

INTERVIEW PROCESS

• 15-minute HR conversation
• Take-home technical assessment
• Technical interview and assessment review with senior ML engineers
• CTO interview
• Executive Committee interview