Mobile Engineer III

Mobile Engineer III

Are you a mobile engineer who thrives on building exceptional user experiences, shipping high-quality apps from scratch, and raising the technical bar for teams around you?

As a Mobile Engineer III at Topstep, you'll play a foundational role in building our mobile trading platform using React Native. You'll be instrumental in launching our MVP, establishing mobile architecture patterns, and then embedding within feature teams to drive ongoing mobile development. This is an opportunity to shape the mobile experience for traders and set the technical foundation that will scale across both our trader experience and trading experience platforms.

This role is ideal for someone who brings both deep React Native expertise and a product mindset. Someone who's excited to own the mobile app end-to-end, establish reusable patterns and components that scale across teams, and work with a team who is building the next generation of our mobile platform. Join us and help define what mobile excellence looks like at Topstep.

Key Responsibilities

• Contribute to the mobile MVP effort to establish our React Native application from the ground up, integrating with GraphQL APIs across our trader experience and trading experience platforms.
• Establish engineering patterns for React Native development, including reusable components, custom hooks, Type Script patterns, and testing strategies that other engineers can adopt.
• Contribute to end-to-end mobile features from design through App Store and Play Store releases, ensuring seamless integration with backend services and optimal performance.
• Partner with product and design to translate trader needs into mobile experiences that balance user experience with technical constraints and platform capabilities.
• Contribute to mobile quality and performance by embedding testing, monitoring, crash reporting, and performance optimization into every feature you ship.
• Embed within feature teams after MVP launch to drive ongoing mobile development, bringing mobile expertise to cross-functional squads.
• Uphold React Native best practices, mobile-specific architectural thinking, and production ownership.
• Champion mobile-first thinking across the organization, helping backend and frontend teams understand mobile constraints and opportunities.

Required Qualifications and Key Competencies

• 3 + years of professional experience building production mobile applications, with demonstrated impact in establishing patterns and practices that scaled across multiple teams.
• Deep React Native expertise, including navigation (React Navigation), state management (Redux, Zustand, Context), native module integration, and performance optimization.
• Strong Type Script and modern JavaScript foundation with understanding of React patterns, hooks, component composition, and functional programming concepts.
• Cross-platform mobile development experience shipping apps to both iOS App Store and Google Play Store, including an understanding of platform-specific differences and capabilities.
• GraphQL client integration experience using Apollo Client or similar libraries, including cache management, optimistic updates, and error handling.
• Strong database fundamentals, including experience with PostgreSQL or SQL Server-schema design, migrations, indexing, and query optimization.
• Mobile-specific performance optimization, including understanding of bundle size, startup time, memory management, list virtualization, and image optimization.
• Production mobile app experience, including crash reporting (Sentry, Crashlytics), analytics integration, remote config, and debugging production issues.
• Testing mindset with experience writing unit tests (Jest), integration tests, and E2E tests (Detox, Appium) for React Native applications.
• Understanding of mobile CI/CD, including automated builds, code signing, Test Flight/Play Store distribution, and release management.
• Track record of technical leadership through architectural documentation, code reviews, component libraries, and establishing mobile engineering standards.
• Excellent communication skills with the ability to explain mobile-specific constraints and trade-offs to varied audiences and build consensus across teams.
• Comfortable making pragmatic decisions, balancing long-term mobile architecture with immediate feature delivery and MVP launch goals.

Preferred Qualifications

• Experience building financial, trading, or fintech mobile applications where real-time data, reliability, and security are critical.
• Background with native iOS (Swift/Objective-C) or Android (Kotlin/Java) development, and understanding when to drop down to native code.
• Experience with real-time data integration using Web Sockets or Server-Sent Events.
• Familiarity with mobile authentication patterns (biometrics, OAuth, secure token storage).
• Experience with complex mobile UI patterns (charts, animations, gesture handling).
• Background building and maintaining shared component libraries or design systems for mobile.
• Experience with Expo or…