Lead Software Engineer

Thermosphr EO Solutions GmbH; Paris; Hybrid; EUR 90,000 - 140,000; Full time

Job summary

Thermosphr EO Solutions GmbH in Paris is seeking a senior backend lead who will split time between hands-on development and technical leadership. You will own architecture, drive real-time data flows, and align product priorities with engineering work.

The role requires strong cloud, IaC, and distributed-systems experience, plus the ability to mentor and grow the team in a hybrid Central Paris setting.

Qualifications

• Senior backend experience with hands-on coding and leadership in production environments.
• Ability to ship features end-to-end and review frontend work credibly.
• Fluent English communication and ability to explain technical topics clearly.
• Proven experience with cloud platforms, IaC, and distributed systems.
• Familiarity with IoT, MQTT, or building automation is a strong plus.

Responsibilities

• Build 60% hands-on backend and cloud infra with robust architecture.
• Own architecture across prototype to production and reduce tech debt.
• Ensure real-time data flows between buildings and cloud with monitoring.
• Translate priorities into technical work and document decisions.
• Lead technical interviews and hire, ramping up the team.
• Contribute to product direction and ship end-to-end features.

Skills

Senior backend experience

Fullstack capability

GCP or cloud (AWS/Azure)

Terraform / IaC

IoT / MQTT familiarity

Networking knowledge

AI-assisted coding tools

Distributed systems

Production-grade code

Leadership in tech teams

English fluency

Tools

Terraform

GCP

Docker

CI/CD

Job description

You are probably senior at a scale-up or a larger company today. You may have recently moved into a management track and found that you miss building, or you may be at the point where the next step is leading people and you want that step to come with code still attached.

This is that role. You lead, you set direction, you own the relationship with the rest of the business, and you stay hands-on. If you want to run a large organisation, we are too small for you. If you want to stop being interrupted, this is the wrong role. If you want the scope of a lead without giving up the work, this is a good fit.

You are not being hired to stop writing code. The split is roughly 60% hands-on engineering, 40% leading technically and aligning.

What you'll do

Build (approximately 60%)

• Implement, maintain, and continuously improve a robust, scalable, high-performance backend and cloud infrastructure.
• Take full ownership of architecture and software development across the full cycle, from prototype to production.
• Ensure stable and reliable real-time data flow between buildings and the cloud, including monitoring and alerting.
• Lead the reduction of technical debt and the consolidation of our platform.

Lead and align (approximately 40%)

• Translate commercial and product priorities from the leadership team and internal stakeholders into technical work, and give an honest read on cost, risk, and sequencing before anything is committed. Write these down. Decisions here are made in short documents, not in meetings, and this bullet is most of what you will be writing.
• Contribute to what we build, not only how. Product direction here is shaped by the people closest to the system, and you will be one of them.
• Grow the team. You will define what we need, run technical interviews, make the call on candidates, and own whether people ramp up well.

The position

You report to the CTO (Aaron) and work alongside two senior software engineers (Sylvain and Tim). You are the technical authority on the platform and the day-to-day lead for the team.

We have no dedicated ops team (yet), so running your own services in production is part of the job. There is no on-call rotation.

This is a hybrid position based in Central Paris, 1-2 days per week on site. The alignment part of this role works better in person, and the people you will be translating for are here.

What you bring

• Professional fluency in English (C1/C2).
• Product judgment. You can tell the difference between a request and a requirement, and you have opinions about what should be built that you are willing to defend and to drop.
• Senior-level experience building and operating back-end systems in critical production environments, including a period as tech lead, lead developer, or the de facto technical owner of a small team.
• Working front-end experience. You do not need to be a front-end specialist, but you need to be able to ship a feature end-to-end without waiting for someone else, and to review front-end work credibly.
• Ability to explain and trivialize technical subjects clearly to non-technical audiences
• Real experience with GCP or an equivalent (AWS, Azure), or a clear willingness to get there fast.
• Analytical and critical thinking, the ability to take responsibility for quality from prototype to production, and the ability to say no.
• Fluency with AI-assisted coding tools (Claude Code and similar), including the ability to critically evaluate AI-generated code and continuously improve internal procedures.
• Comfort with a die and retry philosophy: fail fast in development, rigor in production.
• A genuine interest in producing battle-tested, production-grade code within a distributed environment, and in staying current on software engineering and security.
• Entrepreneurial mindset: you find solutions, take initiative, and accept that at our size responsibilities do not come in neat boxes.
• High bonus: familiarity with IoT, MQTT, or building automation (HVAC).
• High bonus: networking knowledge: routers, VLANs. You will be asked to handle those.
• Ability to challenge existing architectures, including ones that have worked for years.
• True fullstack experience (from prototype to production, any framework, any language) and the ability to maintain a production fleet.
• Infrastructure as code with Terraform.

You are curious and willing to learn. So are we. Even if you do not tick every box, we encourage you to apply.