Defence Account Director

Job Title: Defence Account Director

Location: London; full in-office working as default

Start date: ASAP

Reports to: Founding Defence Lead

Compensation: Salary and Equity options available for discussion

Clearance: Must be eligible to hold UK Security Vetting Clearance SC or above (no prior clearance required)

Application deadline: 01/11/26 at 23:59 UK time

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Help make sovereign AI operational for UK Defence

Cosine is a UK AI lab building models, applications and infrastructure for mission-critical organisations.

We build coding agents, specialised Lumen models, AI-native security products and the infrastructure required to deploy advanced AI in demanding environments. We are also training Lumen Sovereign, the first frontier large language model trained in the UK, with the support of the UK Government.

Defence is a strategic priority for Cosine.

AI will change how Defence operates, from software engineering and intelligence analysis to cyber security, command and control, logistics and frontline operations. The challenge is turning advanced AI into capability that is trusted, secure, sovereign and useful in the real world.

We are looking for a Defence Account Director to help build that business.

This is not a traditional defence sales role. You will understand where Cosine can make a genuine operational difference, identify the right customers and programmes, shape credible opportunities and help turn early conversations into funded pilots, programmes and long-term customer relationships.

You will work closely with Cosine’s Defence Lead, technical teams and senior leadership. You will build relationships across the MOD, the Armed Forces, wider Government and the UK defence industry, while helping define Cosine’s position in the emerging sovereign AI market.

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What you’ll do

Build and own a prioritised Defence account and opportunity strategy.

Develop trusted relationships with senior stakeholders across the MOD, Front Line Commands, wider Government and defence industry.

Identify operational problems, programmes and capability gaps where Cosine can make a material difference.

Translate customer needs into clearly defined use cases, propositions, pilots and programmes.

Navigate Defence stakeholders, budgets, acquisition routes, procurement processes and decision-making structures.

Lead opportunities from initial conversation through demonstration, technical evaluation, commercial agreement and delivery.

Work with Cosine’s technical teams to create credible customer propositions without overpromising.

Develop relationships with primes, strategic partners and specialist technology companies where this creates a stronger route to market.

Maintain disciplined account planning, pipeline management, qualification and forecasting.

Bring structured customer and market insight back to Product, Engineering, ML and senior leadership.

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What we’re looking for

You may have served in the UK Armed Forces or worked closely with Defence in engineering, capability development, acquisition, procurement, digital transformation or technology adoption.

You may subsequently have worked in consulting, technology, industry or an advisory role. What matters is that you understand how Defence works and can turn a customer need into commercial momentum.

You should have:

Meaningful experience of the UK Defence ecosystem.

Strong existing relationships across Defence, Government or industry, and the ability to build new ones.

Experience introducing, acquiring or adopting complex technology.

The ability to structure ambiguous problems and turn them into actionable opportunities.

Strong commercial judgement and comfort being accountable for pipeline, opportunities and revenue.

The confidence to engage with operators, engineers, procurement teams, senior civil servants, military leaders and industry executives.

Genuine technical curiosity and the ability to learn enough about AI to have credible conversations with technical teams and customers.

The resilience to work through long Defence sales cycles while maintaining urgency and focus.

The independence and judgement to operate in a scale-up where the playbook is still being written.

You do not need to be an AI expert when you join. You do need to be intellectually curious, technically literate and able to communicate clearly without hiding behind jargon.

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What success looks like

Success ultimately means winning business and building enduring customer relationships. We aim to onboard at least 10 new client logos within the Defence account over the next 12 months and increase revenues by at least 300%. We expect that growth to come through credibility, judgement, customer insight and persistence rather than transactional selling.

In your first few months, you will:

Build a clear view of Cosine’s Defence proposition, capabilities and priorities.

Establish a focused account and stakeholder map.

Develop relationships with priority customers and partners.

Identify and qualify the most promising opportunities.

Create a disciplined approach to account planning, pipeline and forecasting.

Over time, you will help convert those opportunities into funded demonstrations, pilots and programmes, while shaping how Cosine is understood and adopted across UK Defence.

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Why this role matters

• Defence needs technology that can work across real missions, real systems, real security constraints and real acquisition processes.
• You will help make that happen. This is an opportunity to help build Cosine’s Defence business from the ground up, with direct access to leadership and technical teams and genuine influence over our product, market strategy and customer relationships. If you understand Defence from the inside, have strong customer instincts and want to help make sovereign AI operational, this is an opportunity to have significant impact.

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Why join Cosine

Build a strategically important business from the ground up.

Work at the intersection of frontier AI, Defence and national capability.

Sell a genuinely differentiated product into mission-critical environments.

Influence product direction and go-to-market strategy.

Work closely with a small, technically deep and ambitious team.

Receive meaningful early equity with genuine upside.

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Compensation, Benefits & Ways of Working

We’re an in-office team, five days a week, by design. We believe the work we’re doing benefits from being together, collaborating closely, and building shared context.

What you can expect:

Competitive salary , benchmarked to the market

Equity / share options , so you share in the upside you help create

30 days’ holiday + bank holidays

Work hard in the office, collaborate closely, and switch off properly

Dog-friendly office — bring your dog to work

Weekly team breakfast & lunch

Monthly socials

Pension

High-quality equipment to do your best work

We care about focus, sustainability, and doing great work — not performative overwork. We value people who show up, contribute thoughtfully, collaborate well with their colleagues, and then go home.

This role won’t suit everyone. But if you’re looking for a fast-moving environment, close collaboration, and a team that takes both the work and work-life balance seriously, it’s a great place to be.

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Agency