Founding Backend Engineer

JR United Kingdom; Slough; On-site; GBP 50,000 - 80,000; Full time

Job summary

An early-stage fintech startup is seeking a founding backend engineer to design and build their core platform in London. This high-impact role focuses on developing a modern backend architecture and offers significant ownership and equity potential in a mission-driven environment. Candidates should be experienced in C#/.NET, cloud-native infrastructure, and enjoy working in a fast-paced startup atmosphere.

Benefits

Generous equity options

High-impact role with ownership

Mission-driven environment

Qualifications

• 3+ years experience building backend systems in C#/.NET.
• Experience writing clean, testable code with a TDD mindset.
• Strong grasp of architecture patterns: DDD, CQRS, microservices.

Responsibilities

• Design, build, and launch core platform in C#/.NET 8.
• Help architect scalable systems using modern cloud services.
• Write code daily, influence architectural decisions, and ship fast.

Skills

C#/.NET

Event Sourcing

API Development

Microservices

TDD mindset

CQRS

Clean Code

Tools

AWS

Job description

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We are an early-stage fintech startup (not rebuilding but) re-wiring the global payments infrastructure. Today, sending money across borders is slow, expensive, and fragmented. We're here to fix that—making instant cross-border payments a reality. We’re an early-stage fintech startup, backed by industry insiders, with deep experience in the financial ecosystem. We’re building from zero—no tech debt, no legacy systems. Just a clean slate, strong vision, and higher standards. Now we’re looking for a founding backend engineer to join us at the ground level and help bring this platform to life.

The Role

• You’ll work directly with the founders to design, build, and launch our core platform
• This is a hands-on, high-impact role: you'll write code daily, influence key architectural decisions, and ship fast using modern tools and AI.
• Build a modern backend from scratch in C#/.NET 8 with a clean, event-driven architecture
• Help architect a scalable system using CQRS, Event Sourcing, DDD, microservices
• Own key components in AWS: Lambda, SQS, SNS, DynamoDB, PostgreSQL, API Gateway
• Work in a test-first, high-trust environment with real autonomy

About You

• You work incredibly hard, really care about your work and take pride in what you do
• You ship clean code, scalable systems, and solving complex problems elegantly. You’re excited by ownership and unafraid of ambiguity. You move fast, but with precision.
• You use AI tools to design, code, debug, and ship faster, not just as a nice-to-have but a MUST-have force multiplier

What we're after:

• 3+ years experience building backend systems and APIs in C#/.NET
• Strong grasp of architecture patterns: DDD, CQRS, microservices
• Experience writing clean, testable code with a TDD mindset
• Experience working in small teams or startups, where autonomy and speed matter
• Comfort with cloud-native infrastructure (preferably AWS)

Nice to Have:

• Hands-on experience with event sourcing in production
• Background in payments, fintech, or secure data platforms
• Experience building B2B platforms or financial APIs

Why Join Us?

• Build from 0 to 1: You’ll shape the architecture, team, and product from day one
• Real ownership: You won’t be a cog—you’ll be a core part of the company’s foundation
• Mission-driven: Help reinvent a critical piece of global financial infrastructure
• Equity upside: Generous options in what we believe can be a generational fintech company
• Work with intensity and purpose, in-person with a small team of true builders in London

Why you shouldn't join

• Expectations are incredibly high
• You’re looking for a comfy job with a 40 hour a week commitment with predictable hours and minimal pressure
• You don't see the value in using AI to enhance engineering teams

Logistics

• Location: In-person in London 5 days a week with some flexibility (e.g. remote Fridays)
• Compensation: Competitive salary + high-equity package

To apply please send your CV and a quick note on why you want to join to hello at 3degrees dot co

No visa sponsorship of any kind at this point.