Founding Software Engineer (Senior/Staff) (up to £250k)

Dex; Greater London; On-site; GBP 150,000 - 190,000; Full time

Job summary

Dex is partnering with a stealth startup delivering legal AI services directly to clients. The role involves architecting the core agentic platform, integrating with Slack, Notion, email and CRMs, and enabling in-house lawyers to review and sign off on automated outputs.

You will hire and mentor engineers, set technical direction, and maintain speed and code quality, while shaping the engineering culture at the fastest pace.

Qualifications

• Staff-level engineering experience in fast-moving startups.
• Experience shipping AI-native or agentic systems in production.
• Ability to deconstruct problems into tight MVPs and make foundational decisions.
• Hands-on coding and willingness to stay technically involved.

Responsibilities

• Architect and build the core agentic platform from scratch with zero legacy code.
• Build deep integrations into Slack, Notion, email and CRMs.
• Design human-in-the-loop interfaces and state machines for rapid review and sign-off by in-house lawyers.
• Partner with paying launch customers and internal legal partners to prioritise automation efforts.
• Establish the engineering culture, hire founding engineers, and maintain high code quality.

Skills

Staff-level engineering

AI-native systems

Hands-on coding

Technical leadership

Hiring / mentoring engineers

Tools

Slack

Notion

CRM integrations

Email platforms

Job description

This role is with one of Dex's trusted partner companies. We work closely with their teams to truly understand their culture, goals, and what they're looking for, so we can match you with the right opportunity and give you context about the role before you commit to a process.

The role

Billions have flowed into legal AI, yet the actual service companies receive has barely changed: software is sold to law firms, and the efficiency gains stay with the partners. This stealth startup flips the model by delivering the legal service directly. Their agentic system plugs straight into client workspaces like Slack, Notion, and email to detect legal needs, triage context, and draft roughly 90% of the work, while an in-house team of top-tier lawyers handles the remaining judgement, sign-off, and regulatory liability. Backed by a significant pre‑seed round from top‑tier early‑stage investors, they launch with paying design partners from day one.

The work

• Architect and build the core agentic platform from scratch, establishing the engineering foundations with zero legacy code.
• Build deep, reliable integrations into client workspaces including Slack, email, Notion, and CRMs to capture legal context and drive proactive workflows.
• Design the human‑in‑the‑loop interfaces and state machines that allow in‑house lawyers to rapidly review, verify, and sign off on high‑stakes automated outputs.
• Partner directly with paying launch customers and internal legal partners to identify friction points and decide what to automate first.
• Establish the engineering culture, interview and hire the next founding engineers, and maintain a high bar for speed and code quality.

What You Bring

• Staff‑level engineering capability with a proven track record of taking software products from zero to one inside fast‑moving, venture‑backed startups.
• Demonstrated experience building and shipping AI‑native or agentic systems in production, ideally involving deep integrations into platforms like Slack, Notion, email, or CRMs.
• High‑judgement product sense: you can deconstruct ambiguous problems into tight MVPs, make foundational architectural decisions, and ship fast without over‑engineering.
• Experience setting technical direction and hiring or mentoring other engineers, paired with a clear desire to stay hands‑on writing code.

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