Principal Python Engineer

Location: London, United Kingdom (UK)
Salary: £130,000 per annum

Overview

This role leads the design, development and operational excellence of mission-critical Python services within Financial Services. You will set engineering direction, mentor senior engineers, and partner with stakeholders to deliver secure, resilient and high-performance platforms supporting trading, risk, payments, pricing, or regulatory reporting.

Key Responsibilities

• Own technical strategy and architecture for Python-based systems, ensuring scalability, low latency and reliability.
• Lead design reviews, establish engineering standards, and drive best practice across testing, observability and deployment.
• Build and optimise APIs and event-driven services; integrate with data stores, messaging and third-party providers.
• Champion security-by-design, threat modelling, and secure coding aligned to financial regulatory expectations.
• Collaborate with Product, Quant, Data and Infrastructure teams; translate business requirements into robust technical solutions.
• Improve developer experience through tooling, automation and CI/CD pipelines.
• Provide hands-on delivery, incident support, and continuous improvement across production systems.

Requirements

• Extensive commercial experience with Python (3.x), including performance profiling and optimisation.
• Strong software engineering fundamentals: OO design, SOLID, clean code, code reviews, and documentation.
• Proven experience building distributed systems, microservices, and/or low-latency services.
• Expertise with modern frameworks and tooling (e.g., FastAPI, Django, Flask, Pydantic, SQLAlchemy), plus async Python where appropriate.
• Strong database skills: PostgreSQL and/or other RDBMS; experience with NoSQL and caching (e.g., Redis) beneficial.
• Experience with messaging/streaming (e.g., Kafka, RabbitMQ) and event-driven architecture.
• Cloud and containerisation: AWS/Azure/GCP, Docker, Kubernetes; infrastructure-as-code (e.g., Terraform) desirable.
• Testing discipline: unit/integration/contract tests, TDD where suitable, pytest, mocking, and test automation.
• Observability: logging, metrics, tracing, alerting (e.g., Prometheus, Grafana, OpenTelemetry).
• Security and compliance awareness: IAM, secrets management, encryption, vulnerability management, and audit readiness.
• Strong leadership skills: mentoring, influencing, stakeholder management, and pragmatic decision-making.
• Financial Services experience preferred, with awareness of market data, trade lifecycle, risk, and operational controls.

What You’ll Bring

• A track record of delivering complex platforms in regulated environments.
• Excellent communication skills and a collaborative, ownership-driven mindset.
• Ability to balance speed, quality and risk while maintaining high engineering standards.