iOS-first, Android-optional How You Will Make an Impact ThredUp is transforming the way people shop—and think—about secondhand fashion. Our iOS app is the primary way millions of customers discover and purchase secondhand clothing, making it one of the most critical drivers of our business. As a Senior iOS Engineer, you’ll play a pivotal role in strengthening and evolving this app—stabilizing core systems, modernizing architecture, and shaping new features that deliver seamless and delightful experiences for our users.
Reporting to the Engineering Manager of Core Ecomm, you’ll join a small team working cross-functionally that owns the end-to-end shopping journey—from first-time sign-up through checkout and post-purchase. Your work will directly impact growth and retention, improving reliability while building the foundation for new product innovations.
We are looking for an impact-driven and collaborative engineer who is passionate about delivering stable, performant, customer-focused apps. This candidate should possess the technical excellence and pragmatism to tackle challenging problems, balancing strategic architectural investment with the need to ship fast. In This Role You’ll Get To * Own and improve core areas of ThredUp’s iOS application, ensuring performance, stability, and scalability across critical user flows (onboarding, browsing, checkout, promotions, and post-order). * Leverage crash reporting and performance monitoring tools (e.g., Instruments, Crashlytics, Sentry) to proactively identify and resolve issues. * Collaborate closely with product managers, designers, and engineers across disciplines to deliver impactful features that improve customer trust, conversion, and retention. * Contribute to architectural modernization of the app, introducing patterns and best practices that accelerate development velocity. * Explore strategies to reduce redundant development and improve velocity across mobile platforms (e.g., Kotlin Multiplatform), while maintaining a high-quality native iOS experience.
What We’re Looking For * 8+ years of professional experience developing native iOS applications at scale. * Deep expertise with Swift and Objective-C, with strong knowledge of UIKit and working familiarity with SwiftUI, with experience in modern iOS architectural patterns. * Strong experience with concurrency, memory management, performance tuning, and monitoring & observability. * Proficiency in working with REST and GraphQL APIs, networking, and data integration. * Experience working with continuous integration and release pipelines for iOS applications. * A product mindset: ability to connect technical decisions to user experience and business outcomes. * Curiosity and excitement about leveraging AI to accelerate mobile development (e.g., code generation, testing, performance optimization). * Familiarity with Android (Kotlin/Java) and an interest in collaborating with Android engineers to ensure platform parity is a plus. * Exposure to Kotlin Multiplatform or other shared-code strategies, along with experience in consumer-facing e-commerce, search, or other high-scale user engagement applications is a plus. * Experience mentoring peers or leading feature-level initiatives is a plus.
