Senior .NET Developer (FIX Protocol) .Net · Poland ·

Avenga; Polska; Hybrid; PLN 180,000 - 320,000; Full time

Job summary

Avenga seeks a strong backend engineer in Poland for a FinTech-focused role. You will design and build scalable microservices using .NET, MongoDB, Redis, RabbitMQ, Pulsar, and Elasticsearch, collaborating in a 7-person team with exposure to React frontend.

You should have 5+ years in backend, deep C#/.NET, APIs, distributed messaging, FIX protocol experience in capital markets, and finance-related modeling with QuantLib. This is hands-on and high-impact.

Qualifications

• 5+ years of backend development experience.
• Strong C#/.NET and API design expertise.
• Experience with distributed messaging systems and event-driven architectures.
• FIX protocol experience in capital markets or electronic trading.
• Knowledge of financial calculations, pricing engines, or quantitative models.
• Hands-on with QuantLib or similar libraries.
• OAuth2 / OpenID Connect authentication experience.
• Experience with MongoDB or other NoSQL databases.
• Exposure to capital markets, fintech, trading platforms, or fixed income.

Responsibilities

• Design and develop high-quality backend services using C#/.NET.
• Build scalable ASP.NET service-side applications with reliability.
• Work with distributed messaging frameworks and event-driven architectures.
• Develop and optimize data solutions using NoSQL databases like MongoDB.
• Design and implement financial calculation engines and pricing models.
• Implement FIX protocol integrations for electronic trading workflows.
• Define identity and authorization solutions across backend services.
• Collaborate with product, frontend, and DevOps teams on deployment strategy.
• Mentor engineers and uphold coding standards.

Skills

Backend development

C#/.NET

API design

Distributed messaging

Event-driven architectures

FIX Protocol

Quantitative finance

QuantLib

OAuth2/OpenID

MongoDB

Capital markets

Tools

MongoDB

Redis

RabbitMQ (MassTransit)

Pulsar

Elasticsearch

Datadog

Sentry

React

Redux

Job description

Avenga is an international engineering firm helping businesses operate with AI at the core. With 6,000+ experts worldwide, we combine engineering expertise with AI-native thinking to turn ambitious ideas into real-world impact across industries, technologies, and markets.

At the core of the role

We are looking for strong backend engineer with experience in the FinTech domain, working on a microservices and event-driven architecture based on .NET, MongoDB, Redis, RabbitMQ (MassTransit), Pulsar, and Elasticsearch. Experienced in designing scalable distributed systems and collaborating within a 7-person engineering team. Additionally exposed to React development.

Core skills you’ll bring

• 5+ years of backend development experience
• Strong C#/.NET (Java may be considered)
• Experience building and designing APIs
• Distributed messaging systems and event-driven architectures
• FIX Protocol experience in a capital markets / electronic trading environment
• Experience with financial calculations, pricing engines, or quantitative models
• Hands-on experience with QuantLib (or similar quantitative finance libraries)
• OAuth2, OpenID Connect, IdentityServer or similar authentication frameworks
• MongoDB or other NoSQL databases
• Experience in capital markets, fintech, trading platforms, fixed income, securities pricing

Nice-to-have

• Datadog, Sentry, Elasticsearch
• SignalR / WebSockets
• Pulsar, Databricks, Lakehouse
• React + Redux (nice to have)
• Experience mentoring engineers / technical leadership

The impact you'll create

• Design and develop high-quality backend services using C#/.NET
• Build and maintain ASP .NET service-side applications with a focus on scalability and long-term reliability.
• Work with distributed messaging frameworks and event-driven architectures to support high-throughput trading systems.
• Develop and optimize data solutions using NoSQL databases such as MongoDB.
• Design and implement financial calculation engines, pricing models, and quantitative algorithms with a strong emphasis on accuracy and performance.
• Implement and maintain FIX protocol integrations to support electronic trading workflows.
• Design and enforce identity, authentication, and authorization solutions across backend services.
• Integrate and work with observability platforms such as Datadog or Elasticsearch to support system monitoring and diagnostics.
• Ensure numerical precision in financial computations, including proper handling of rounding, accruals, and market conventions.
• Collaborate with product, UI/UX, frontend, and DevOps teams to align on development and deployment strategy.
• Build reusable, testable backend infrastructure and uphold consistent coding standards across teams.
• Implement telemetry and monitoring best practices using Sentry or equivalent tools.
• Evaluate and adopt new technologies, frameworks, and design patterns to continuously improve engineering outcomes.
• Mentor engineers on backend development best practices and foster a culture of engineering excellence.
• Contribute to frontend solutions using React and Redux/Rematch where needed. (nice to have)

People are at the core of Avenga. We provide equal opportunities regardless of race, ethnicity, gender identity, sexual orientation, disability, age, religion, or any other characteristic. We are committed to a respectful environment where everyone can be themselves, share their ideas, and feel that they belong.