Founding Data EngineerLondon – Hybrid (3 days) - £70,000-£80,000 + meaningful equityCompanyOur client is a London-based, well-funded startup specialising in analytics and predictive ML models. They help mobile apps optimise ad spend by analysing behavioural data and delivering predictive signals for high-value conversions. As the first data engineer, you’ll work directly with the founders to build core data infrastructure that powers real business impact.Responsibilities As the founding Data Engineer, you will own the design and implementation of data pipelines and infrastructure, including:Build production ETL pipelines processing millions of mobile analytics events from MMPs like AppsFlyer and AdjustEngineer features for ML models, including temporal patterns, user behaviour sequences, and campaign attributionEnsure data quality via validation, deduplication, schema checks, and defensive programmingOptimise pandas/Polars pipelines for performance at scaleHandle messy real-world data: duplicates, nulls, schema drift, and out-of-order eventsBuild and orchestrate pipelines using Prefect and monitor BigQuery operationsEstablish CI/CD practices and maintain clean, maintainable codeIntegrate APIs with MMPs and advertising platforms, and collaborate with data scientists to productionise ML modelsSet data quality standards and influence the technical strategy for the platformRequirements4–6+ years of building production data pipelines with measurable business impactDeep expertise in Python, SQL, and pandas, with experience in memory optimisation and vectorisationExperience managing messy real-world data and maintaining high data quality standardsStrong code quality practices (e.g., ruff, mypy, pytest, SQLFluff, pre-commit)Right to work in the UK and ability to work 3 days/week from Central London officeStrong problem-solving skills, attention to detail, and ability to work independentlyExperience with workflow orchestration (Prefect, Airflow, Dagster), cloud data warehouses (BigQuery, Snowflake), or backend Python frameworks (Django, FastAPI) is a plusBenefits25 days annual leave plus bank holidaysMeaningful equity options as the first engineering hireFlexible working: 3 days/week in London office, remote otherwiseLearning budget for courses, conferences, and professional developmentDirect founder-adjacent experience with strategic inputOwnership of core systems from near-scratch with full autonomyImmediate impact: your code drives production outcomes and company revenueOpportunity to shape engineering culture and grow with the company