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

Dex; Greater London; On-site; GBP 110,000 - 140,000; Full time

Job summary

Dex’s trusted partner company is building a stealth startup that delivers legal AI services by integrating with client workspaces like Slack, Notion, and email to draft the majority of tasks while lawyers handle high-stakes decisions. The role focuses on architecting the agentic platform and establishing the engineering foundations with zero legacy code.

You will design human-in-the-loop interfaces, work closely with launch customers and internal legal partners, and help shape the engineering

Qualifications

• Staff-level engineering capability with a track record of taking software products from zero to one in fast-moving startups.
• Experience building and shipping AI-native or agentic systems in production, with deep integrations to platforms like Slack, Notion, email, or CRMs.
• High-judgement product sense: deconstruct ambiguous problems into tight MVPs and make foundational architectural decisions.

Responsibilities

• Architect and build the core agentic platform from scratch, establishing 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 human-in-the-loop interfaces and state machines for in-house lawyers to review, verify, and sign off on high-stakes automated outputs.
• Partner with 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.

Skills

Staff-level eng

AI-native systems

Architectural decisions

Hiring engineers

Hands-on coding

Tools

Slack

Notion

CRM integrations

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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