Senior Backend Engineer

Fi; Greater London; Hybrid; GBP 90,000 - 130,000; Full time

Benefits offered by this job

Equity options

Pension

Private Medical Insurance

25 days holiday

Hybrid work model

Work abroad

Job summary

9fin is seeking a Senior IC Engineer to own systems design and drive backend development in a cross-functional team. You will mentor junior engineers and shape data flows from storage to API endpoints, applying best-practice validation and testing.

You’ll work on Python-based backend services (FastAPI) on AWS, with automated tests, and a strong emphasis on code quality and collaboration across product, client success, and editorial teams.

Qualifications

• This role requires a Senior IC Engineer who can lead systems design and mentor teammates.
• Plan and reason about software with clear business impact and cross-functional input.
• Experience designing data flow from storage to API endpoints with validation practices.

Responsibilities

• Lead projects by defining systems, building proof-of-concepts, and delivering new backend features.
• Collaborate with Product and Clients on API development and data processing pipelines.
• Mentor junior developers, conduct code reviews, and contribute to early R&D.

Skills

Senior IC Engineer

Mentoring juniors

Python

FastAPI

API design

SQL

Cross-functional collaboration

Tools

Python

PostgreSQL

Job description

About 9fin

9fin is the AI platform powering global debt markets — the world’s largest asset class at over $145 trillion. Debt markets are vast, global, and mission-critical, yet still run on fragmented data, PDFs, and manual workflows. 9fin replaces this broken infrastructure with a single platform that centralises proprietary credit data, deep analysis, and high-value workflows across global markets. Today, 9fin powers teams at 300+ blue-chip institutions worldwide, including global banks, asset managers, private equity firms, law firms, and advisors. The business is scaling at exceptional speed, with rapid expansion in the US and best-in-class retention driven by deep workflow adoption. We’re at a defining inflection point. With proven product-market fit and strong, global market pull, 9fin is accelerating toward becoming the category-defining platform for debt markets worldwide.

What you'll work on

The team maintains a strong focus on impact, using technology to deliver value for the business. While we have a high-level vision from the business, we have autonomy to set our team goals and define our own success. We take responsibility for our outcomes and emphasize proactive behaviours like ownership and accountability.

• As part of a cross functional team, lead projects by defining and designing systems, building proof of concepts, and delivering new service functionality
• including APIs, data processing and automation while collaborating with Product and Clients - Development and engineering primarily on the backend services and web application hosted tools and systems of the 9fin platform.
• Play an impactful role within project teams as a senior IC, running code reviews, mentoring other developers, leadership & involvement in early research and experimentation with new technologies providing input for new features and products.
• Continually improve the 9fin codebase taking the chance to automate, refactor and document when it’s most impactful.
• Very diverse web platforms, from complex financial data modelling, complex access control business logic, capturing environmental, emission, energy data, incorporation of ML/AI prediction services, data visualisation serving and automation systems.
• Collaboration and teamwork: Cross functional teams are formed for all projects including the appropriate domain expertise from 9fin financial, legal and editorial colleagues. This allows the best quality information and feedback to go directly to engineering project teams.
• Your ability to explain and break down complex projects to non technical audiences will enable productive and efficient team progress.
• Developer Experience: Through managed automated preview environments, feature flags and well maintained non production environments. You will be able to move with velocity and get feedback and iterate quickly.

Our Backend Stack

• Python is the dominant backend language used
• Flask & FastAPI
• Typing is used within our Python stack to power automated documentation and API definitions
• Relational Databases (PostgreSQL) at the heart of majority of services
• We have our own internal developer platform with standardised paved road approaches to infrastructure to bring your code into production as quickly as possible.
• We’re AWS for Cloud hosted services
• Heavy use of AWS lambda Serverless
• Docker (AWS ECS) for uniform development/deployment from dev to prod

Requirements

This role will be a great fit if you:

• Have experience operating as a Senior IC Engineer, leading systems design and infrastructure discussions, mentoring more junior team members, and scoping work within cross-functional product teams.
• Plan and reason about software effectively, clearly and compellingly communicating its purpose within systems and its business impact on clients
• Have hands‑on experience designing data flow through software, from persistent storage to API endpoints, while applying industry best practices for validation
• Experience with Python and its web frameworks (we currently use FastAPI with strong typing & Pydantic)
• Strong experience delivering APIs, Service Oriented Architecture
• Strong working knowledge of SQL statements for retrieving data
• A good collaborator and communicator with cross functional engineering teammates and others within 9fin
• Code Quality: Through writing testable, maintainable code, and by engaging in code review for your own work and for reviewing others

Nice-to-have: - Experience in data modelling and with a pipeline orchestrator

Benefits

• We’re a scaling start up and we enjoy sharing our success, when the company succeeds, we always reinvest that in our people. We also offer huge amounts of responsibility, an abundance of opportunity for growth and a platform to truly excel.
• Financial & Insurance - Competitive Salary (our salary bands are benchmarked at the top end of the market)
• Equity options
• Pension (your minimum contributions are 4% with 9fin matching up to 7%)
• Private Medical Insurance
• Paid sick leave with Income Protection for long periods of illness
• Group Life Assurance
• Season Ticket Loan & Cycle to Work schemes
• Time off - 25 holiday days per year
• Local public holidays (with the ability to exchange them for alternative days)
• Hybrid working model, to allow you the flexibility to decide how, where and when you do your best work
• Work abroad for up to 3 months a year
• 1 month paid sabbatical after 5 years of service
• Enhanced parental leave & flexible working arrangements available
• Training & Culture - Professional learning and development budget
• Quarterly team socials
• Summer and Winter company social events

9fin is an equal opportunities employer

At 9fin we are dedicated to building and promoting a fair and inclusive workplace where everyone can reach their full potential and truly belong. We recognize that building diverse teams enables a more creative and productive environment.

If you’re excited about this role but your experience doe