Senior Software Engineer - Growth

At Klaviyo, we value the unique backgrounds, experiences, and perspectives each Klaviyo brings to our workplace. We believe everyone deserves a fair shot at success and appreciate the experiences each person brings beyond traditional job requirements. If you’re close but not an exact match, we hope you’ll still consider applying. Want to learn more about life at Klaviyo? Visit klaviyo.com/careers to see how we empower creators to own their own destiny.

Why You Should Join the Onboarding Team

The Product Expansion / Activation team is focused on improving the early experience of Klaviyo for new customers. We work diligently to improve the rate at which customers are successfully setting up their Klaviyo account and gaining value from the platform. Engineers use data to discover opportunities, implement A/B tests, and work across the product to iteratively improve UX and reduce friction for new customers. We are looking for great generalist software engineers with a passion for the experience layer and an interest in growing a user‑base and building a great customer onboarding pipeline and experience.

How You Will Make a Difference

• Drive the technical design and lead the implementation of high‑impact user‑experience improvements across Klaviyo, focusing on areas critical to new customer success and adoption. Own the entire project lifecycle, working through ambiguity and requirements refinement to execution and delivery.
• Own the end‑to‑end experimentation process, contribute to strategy definition, architect and implement A/B tests to validate product hypotheses, and interpret data to drive significant iterative improvements. Be accountable for the quality and operational health of features delivered.
• Serve as a technical leader and liaison, collaborating proactively with partners across teams to define and prioritize key technical initiatives and shape the long‑term roadmap.
• Mentor and provide technical guidance to other engineers, elevating experimentation, development, and operational practices, ensuring contributions consistently leave the product area better than before.
• Define the architectural approach and technical strategy, anticipating scalability and reliability needs, leveraging AI agents where appropriate, and ensuring solutions are robust, scalable, and adhere to best practices for security, performance, and maintainability.
• Work from our Boston HQ at least three days a week.

Who You Are

• Have an extensive background in full‑stack software engineering, with deep understanding of Klaviyo’s systems and the ability to architect, deliver, and maintain high‑scale, user‑facing features and supporting APIs.
• Demonstrated ability to drive technical strategy and improvement using a data‑driven mindset, leading to measurable business results and upholding best practices.
• Experience with AI‑driven software delivery practices and championing them, a passion for continuous learning and mentoring, and the ability to guide others to project success.
• Experience driving A/B testing strategies for metric‑based goals that improve user experience, customer acquisition, and success.
• Thrives in an entrepreneurial, customer‑focused environment, bringing clarity and technical stability to ambiguous challenges and prioritizing work that enables the team to move faster.

Technologies We Use (not Exhaustive)

• HTML, TypeScript, JavaScript, React
• Python, Django
• MySQL, Cassandra, RabbitMQ, Redis
• Amazon Web Services (EC2, RDS, Aurora, etc.), Terraform, Ansible, Packer, and other DevOps tools

Massachusetts Applicants: It is unlawful in Massachusetts to require or administer a lie detector test as a condition of employment or continued employment. An employer who violates this law shall be subject to criminal penalties and civil liability.

Base Pay Range for U.S. Locations: $148,000—$222,000 USD. In addition to base salary, total compensation may include participation in the company’s annual cash bonus plan, variable compensation for sales and customer success roles, equity, sign‑on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility.

This role may require up to 10% travel for purposes such as new hire onboarding, client or partner work, team meetings, and industry events. Travel is coordinated in advance.

Klaviyo is committed to a policy of equal opportunity and non‑discrimination. We do not discriminate on the basis of race, ethnicity, citizenship, national origin, color, religion or religious creed, age, sex (including pregnancy), gender identity, sexual orientation, physical or mental disability, veteran or active military status, marital status, criminal record, genetics, retaliation, sexual harassment, or any other characteristic protected by applicable law.