Principal Software Engineer Engineering Belfast / Hybrid

Joulen; Belfast City District; Hybrid; GBP 120,000 - 180,000; Full time

Benefits offered by this job

22 days annual leave plus 11 holidays

Option to buy additional annual leave

Pension

Life Assurance

Private Medical Insurance

Job summary

Joulen in Belfast is seeking a Principal Software Engineer to act as the senior technical authority across product domains, shaping design principles, delivery strategy and operational standards while remaining hands-on.

You will mentor other engineers, advance trunk-based development, and govern AI-driven systems, with ownership of production reliability and collaboration with Head of Engineering to scale Joulen's energy-market platform.

Qualifications

• Demonstrable, hands-on XP: TDD, DDD, pair and mob programming, refactoring
• Track record of defining CD strategy with trunk-based development and feature flags
• Experience setting design principles, test strategy, and operational standards across multiple systems

Responsibilities

• Be the technical authority for your product domain and align engineering with product propositions
• Set standards to keep systems simple, tested, and safe to change at scale
• Shape continuous delivery and release strategy for frequent production deployments
• Own production reliability and govern AI in production software
• Design team interaction models and establish code ownership and review norms
• Grow senior engineers and influence hiring
• Collaborate with leaders to communicate up to board level

Skills

Technical leadership

Hands-on coding

TDD/XP

System architecture

AI in production

SDLC governance

Team Topologies

Hiring & mentoring

Energy markets domain knowledge

Tools

Git

CI/CD

Observability tools

Job description

The energy system is changing fast. As renewable generation and electrification spread, flexibility becomes more valuable, and assets such as home batteries, commercial and industrial batteries, electric vehicles and grid-scale storage can all help balance supply and demand. Capturing that value takes direct market access, sophisticated forecasting and real-time optimisation.

Joulen provides all three. We trade directly in energy markets and use our platform to forecast tradable volumes and find the strongest opportunity in any given period, so flexible assets earn more than they otherwise would. We do this with installers, energy retailers and OEMs, who gain a stronger customer proposition and a new revenue stream, while asset owners see better returns and the grid gets more flexibility.

The role

As a Principal Software Engineer you are the senior technical authority for one or more of Joulen's product domains, sitting between Senior Engineer and Head of Engineering on our Software Engineer career track. You set the design principles, delivery strategy and operational standards for your domain, and you work with the other Principals & Head of Engineering to shape how engineering works across Joulen.

You stay hands-on: you pair, write tests first and ship small increments to trunk like everyone else. Your leverage comes from turning GB energy-market change into sound platform and architecture decisions, and from growing other senior engineers.

Key Responsibilities

• You will be the technical authority for your product domain, and the person who understands the relationship between your engineering domain and product propositions it serves. That means understanding our products such as Flex, Trade and Grid.
• You will set the standards that keep our systems simple, tested and safe to change at scale. You define the design principles, test strategy and coding standards for your domain, own its technical-debt strategy, and arbitrate the significant trade-offs between systems.
• You also shape our continuous delivery and release strategy, so that engineers can ship small changes to production frequently and confidently.
• You will own the reliability of what we run and how we use AI to build it. You set operational standards and the incident framework for your domain, and you help lead Joulen's agent engineering practice, including how AI is governed in production software.
• Beyond your own systems, you will shape how engineering works across Joulen. With the other Principals you will design team interaction models for fast flow, build the ownership and review norms that keep the codebase collectively owned, and set the standard for how engineering communicates, up to board and external audiences.
• You will grow other senior engineers, influence hiring, and help keep a culture where problems surface quickly and are resolved without politics
• Demonstrable, hands-on Extreme Programming practice: TDD, DDD, pair and mob programming, continuous refactoring and simple, emergent design.
• A track record of defining continuous delivery strategy with trunk-based development, feature flags and progressive delivery.
• Experience setting design principles, test strategy and operational standards across several systems or teams, not just your own.
• Ownership of production reliability: observability, incident frameworks and reducing MTTR.
• Fluent AI-native engineering, with a view on governing AI and agent-driven systems in production.
• Working knowledge of Team Topologies and how team boundaries shape architecture and flow.
• Clear, persuasive writing (ADRs, strategy papers, postmortems) for engineers, commercial colleagues and board-level readers.
• A history of developing senior engineers and shaping hiring.
• Experience in GB electricity markets, flexibility, trading, dispatch or settlement. If you don't have it yet, you'll need the appetite to become an authority quickly.
• Experience designing platforms and systems for agentic or AI-assisted delivery.
• A profile in external software engineering or energy-industry forums.

What we offer

• 22 days annual leave plus 11 public holidays
• Option to buy additional annual leave
• Pension
• Life Assurance
• Private Medical Insurance

How We Work

Joulen runs on six operating principles: Customer Centricity, Talent Density, Move with Urgency, Radical Candour, Disagree & Commit, and Owner-Operators. In practice that means you will be given the outcome and the autonomy to get there, you will get direct feedback and be expected to give it, and you will be trusted to make decisions in your area without waiting for permission.

New joiners go through Joulen Bootcamp, our structured onboarding programme, so you will understand the energy markets we operate in and how our product works, not just the ledger.