Principal Engineer

Principal Engineer

Help us build an AI-native platform where segmentation, analysis and activation happen through conversation, not configuration. Lexer is a Customer Data Platform that's been helping retail and hospitality brands understand and act on their customer data for seventeen years. We're now rebuilding what a CDP can be: an AI-native platform where the hard work of segmentation, analysis, and activation happens through conversation, not configuration. That's a significant engineering undertaking, and it changes what great engineering looks like here.

We're looking for a Principal Engineer to work with our AI product teams on the hardest technical problems we have. This is the most senior individual-contributor engineering role at Lexer. You'll shape how the engineering organization builds, through demonstrated technical authority and the quality of the systems you create. You'll work across every stream, taking on the highest-leverage problems and lifting the standard of engineering around you.

At its core this is a software engineering role. You're building and operating a SaaS and data platform product that our customers rely on every day — multi-tenant, always-on, and held to a high bar for quality, performance and reliability. Strong software engineering fundamentals are the foundation everything else here is built on. We've transitioned to agentic harness engineering and spec-driven development, where engineers direct AI agents and maintain the systems that produce software rather than writing all of it by hand. You work fluently this way and you push the practice forward, building the guardrails, specifications, and architectural practices that let agents move at speed without eroding the system.

Role details:

• Level: Principal Engineer — the most senior individual-contributor role in engineering.
• Reports to: CTO.
• Experience: 8+ years of hands-on software engineering, including significant time operating at a senior/staff level across complex systems.
• Location: Remote or Hybrid — Melbourne-based, hybrid (3 days a week in our St Kilda office, 2 days working from home). Remote considered with strong overlap with AEST/AEDT core hours.

How we work:

We practice spec-driven development inside an agentic harness: engineers direct AI agents and maintain the systems that produce software. Our engineering culture draws on XP — test-first, continuous integration, small batches, pairing, and shared ownership. This is a hands-on, collaborative role.

Our stack: Predominantly Python and React, running on AWS, with data processing in Databricks.

What you'll do:

• Work hands-on across engineering streams on the AI capability layer, the data contracts that hold the platform together, and the ongoing modernisation of the platform.
• Hold architectural direction as a living function; own the ADR process.
• Keep the architecture adaptable (low coupling, high cohesion, strong boundaries).
• Design for reliability and observability from the start.
• Build the guardrails that keep agentic engineering safe at speed, including spec-driven development, architectural practices, context engineering, and test coverage.
• Lift the engineers around you through pairing, code review, and the standard your own work sets.

What success looks like:

• In your first 3 months: Hands-on in the team building our new AI flagship product; strong contributor shipping toward PMF; adapting the agentic harness; running the ADR process.
• By 6 months — caretaker of scale: Systems adaptable for new opportunities, the right amount of rigour and process, ensuring infrastructure is fit for purpose.
• By 12 months — across the whole platform: Working across multiple teams to ensure the holistic platform fits together coherently; recognised as a technical authority who raises the bar across engineering.

What you'll bring:

• Must haves:
• Strong software engineering fundamentals; track record building, shipping and operating production SaaS at scale; clean, well-tested, maintainable code and healthy CI/CD.
• Deep hands-on engineering across complex systems, ideally with data-intensive or platform work.
• Practical experience directing AI coding agents to ship production software, and building guardrails and architectural practices that make it safe at scale.
• A track record of holding architecture across a whole system, not just a single team.
• Strong communication; ability to make complex technical directions clear to engineers and non-engineers; can model and communicate designs visually, including with C4.
• Comfort working in a mature, evolving codebase; able to navigate real complexity and still move fast.
• Strength across our stack: Python (or similar), React and AWS.
• Strong preference:
• Background in CDP, martech, or data platform domains.
• A foundation in SOLID architectures and XP-style practice — test-first, continuous integration, small batches, shared ownership.
• Nice to haves:
• Experience re-platforming legacy stacks toward modern architectures.