Senior Principal Engineer

About the role

Trainline is a leader in the rail and coach travel sector, serving millions of users across Europe. This role sits within the App Platform team, where you will define the technical direction for our iOS ecosystem while collaborating with peers across Android, Web, and Architecture. You will own the long-term technical strategy for iOS to support company business objectives and ensure that engineering efforts directly enable growth and reliability. In this capacity, you will create and maintain engineering standards and reusable patterns that improve developer experience and software quality across the organisation. The position requires you to lead large-scale modernisation initiatives designed to increase system maintainability and delivery speed over time. You will collaborate with architects and engineering leaders to build a unified cross-platform strategy that balances platform-specific strengths with shared goals. A core part of the role involves promoting modular, testable, and sustainable software design across all engineering teams working on customer-facing features. You will assess new technologies and AI-driven tools to determine their value regarding security, cost, and operational impact for the business. Through technical proposals and evidence-based discussions, you will influence stakeholders across product, design, and executive leadership. Mentoring senior engineers and contributing to the growth of the Principal Engineering community is also part of the position, ensuring knowledge transfer and career development.

Key facts

What you'll do

• Establish and own the long-term technical strategy for iOS to support company business objectives and align roadmap decisions.
• Create and maintain engineering standards and reusable patterns to improve developer experience, code consistency, and software quality.
• Lead large-scale modernisation initiatives that refactor legacy codebases and improve system maintainability and delivery speed.
• Collaborate with architects and engineering leaders to build a unified cross-platform strategy that leverages platform-specific capabilities.
• Promote modular, testable, and sustainable software design principles across all engineering teams to reduce technical debt.
• Assess new technologies and AI-driven tools, performing in-depth evaluations regarding security, cost, and operational impact before adoption.
• Influence stakeholders across product, design, and executive leadership through clear technical proposals, data, and roadmap insights.
• Mentor senior engineers, providing guidance on technical decisions, career growth, and best practices in software engineering.
• Contribute to the growth of the Principal Engineering community by sharing knowledge, building internal frameworks, and enabling scalability.
• Define and evolve best practices for iOS development, ensuring alignment with industry standards and emerging patterns.
• Drive the adoption of cross-platform architectural strategies while respecting the unique needs of iOS and its integration points.
• Evaluate and integrate AI-enabled engineering practices that enhance productivity without compromising code quality or security.
• Partner closely with product managers to translate business requirements into technical specifications for iOS applications.
• Ensure that delivered solutions are robust, maintainable, and scalable to meet current and future demands of the business.

Requirements

• Extensive experience defining technical strategy for large-scale iOS products in a production environment.
• Deep technical knowledge of modern iOS development, including Swift, UIKit, and SwiftUI, as well as runtime behaviours.
• Deep understanding of modular software architecture and how to design systems that scale across teams and products.
• Demonstrated ability to set engineering standards and drive their adoption across an organisation of multiple teams.
• Proven track record of aligning engineering disciplines, including iOS, Android, Web, and Architecture, with product and design goals.
• Strong decision-making skills regarding the integration of emerging technologies and AI tools into the engineering workflow.
• Advanced communication skills capable of engaging both technical staff and executive leadership with clarity and confidence.
• Experience working in a hybrid environment where asynchronous and synchronous collaboration across time zones is common.
• Familiarity with security best practices and how they apply to mobile application development and third-party integrations.
• Understanding of how to measure the impact of technical decisions on business outcomes, user experience, and engineering efficiency.
• Commitment to maintaining high standards of code quality, testing, and documentation across the iOS codebase.
• Willingness to work closely with cross-functional partners to resolve dependencies and unblock critical delivery paths.

Nice to have

• Active participation in the wider iOS engineering community through public speaking, open-source contributions, or mentoring.

Practical notes

• This is a hybrid role requiring office attendance for at least 60% of your time over a 12-week period.
• Benefits include private healthcare, dental insurance, an EV scheme, 2-for-1 share purchase plans, and extra festive leave.
• Employees are eligible for a 28-day work from abroad policy.
• The company provides personal learning budgets and dedicated learning days for career development.

About the company

We are champions of rail, inspired to build a greener, more sustainable https://www. thetrainline. com/terms/sustainability-faqs future of travel.