Senior iOS Engineer

About the position

About ThredUp

ThredUp is transforming resale with technology and a mission to inspire the world to think secondhand first. By making it easy to buy and sell secondhand, ThredUp has become one of the world's largest online resale platforms for apparel, shoes and accessories. Sellers love ThredUp because we make it easy to clean out their closets and unlock value for themselves or for the charity of their choice while doing good for the planet. Buyers love shopping value, premium and luxury brands all in one place, at up to 90% off estimated retail price. Our proprietary operating platform is the foundation for our managed marketplace and consists of distributed processing infrastructure, proprietary software and systems and data science expertise. With ThredUp’s Resale-as-a-Service, some of the world's leading brands and retailers are leveraging our platform to deliver customizable, scalable resale experiences to their customers. ThredUp has processed over 172 million unique secondhand items from 55,000 brands across 100 categories. By extending the life cycle of clothing, ThredUp is changing the way consumers shop and ushering in a more sustainable future for the fashion industry.

Recognized on TIME’s Best Inventions 2024, TIME's Most Influential Companies of 2023,  Digiday's WorkLife 50 2023, TIME's Best Inventions of 2022, and Lattice's People Success Awards 2022.

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.

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What We’re Looking For:j

• 5+ 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.

This role is not eligible for visa sponsorship.

What We Offer:

• 4-day work week, with Fridays off

• Hybrid work environment: 3 days in the office and 1 day remote each week

• Competitive salary (we leverage market data)

• Many ThredUp employees also have the opportunity to own shares of ThredUp stock and are eligible for discretionary restricted stock unit awards

• Employee stock purchase plan

• Flexible PTO (take the time you need) + 13 company holidays

• Paid Sabbatical after 3 years of full time employment

• Generous paid parental leave for new mothers and fathers

• Medical, dental, vision, 401k, life and disability insurance offered

• We live by our Core Values of Transparency, SpeakingUP, Thinking Big, Infinite Learning, Influencing Outcomes & Seeking the Truth

We believe diversity, inclusion and belonging is key for our team

At ThredUp, our mission has been built on extending the lives of millions of unique clothing items. Much like our inventory, we are proud to have fostered a workplace that is one-of-a-kind. As a company focused on diversity, inclusion and belonging, we are committed to ensuring our employees are comfortable bringing their authentic selves to work every day. A unique perspective is critical to solving complex problems and inspiring a new generation to think secondhand first. Be you.

If you are a candidate with a disability and have a reasonable accommodation request for the job application process, please email disabilitysupport@ThredUp.com the specific details of your disability related accommodation request. This email address is reserved for candidates with disabilities only. General application inquiries will not receive a response.

Place of work