Senior .NET Engineer – API & Systems Architecture

OneMain Financial; West Valley (WA); On-site; USD 90,000 - 130,000; Full time

Job summary

OneMain Holdings, Inc. is seeking an experienced .NET software engineer to contribute to the architecture and development of enterprise-grade systems, including loan origination and servicing platforms.

You will work on scalable, secure backend services and customer-facing web apps. The role requires 3–5+ years in .NET, strong T-SQL/C#, and hands-on experience with WPF/XAML, WebAPI, and modern frontend connections.

Qualifications

• 3–5+ years of experience developing enterprise-grade applications in .NET.
• Strong skills in T-SQL, C#, and backend service design.
• Understanding of distributed systems and multi-tier architectures.
• Hands-on experience with WPF/XAML, LINQ, MVVM, and WebAPI; exposure to React or Angular is a plus.
• Proficiency in RESTful API design, JSON, and XML integrations.
• Ability to explain technical concepts clearly across teams.
• Experience working in Agile environments with DevOps practices.

Responsibilities

• Contribute to the architecture and development of key systems including Loan Origination Systems, Loan Servicing Systems, and customer-facing applications (e.g., omfauto.com, foursight.com, rateworks.com).
• Ensure scalable, maintainable, and secure software design within assigned projects.
• Implement APIs, middleware services, and integrations with internal and external tools such as Twilio Flex.
• Collaborate with peers through code reviews, design discussions, and pairing sessions.
• Support automation and continuous integration strategies to improve development efficiency and reliability.
• Assist in technical initiatives to modernize legacy systems and improve scalability.
• Participate in troubleshooting and performance tuning to maintain system health.

Skills

.NET development

Backend service design

T-SQL

C#

WebAPI

WPF/XAML

MVVM

LINQ

React or Angular

Agile with DevOps

Mentoring peers

Distributed systems

Multi-tier architectures

Education

Bachelor’s degree in Computer Science, Engineering, or related field

Tools

WPF/XAML

LINQ

MVVM

WebAPI

JSON

XML

Job description

OneMain Holdings, Inc. is seeking an experienced .NET software engineer to contribute to the architecture and development of enterprise-grade systems, including loan origination and servicing platforms.

You will work on scalable, secure backend services and customer-facing web apps. The role requires 3–5+ years in .NET, strong T-SQL/C#, and hands-on experience with WPF/XAML, WebAPI, and modern frontend connections.