Cyber Security Lead

REX Cyber Security; Greater London; Hybrid; GBP 110,000 - 140,000; Full time

Job summary

REX Cyber Security, a leading UK professional services firm, seeks a Cyber Security Architect & Engineering Lead to own security across Microsoft 365, Azure, Entra ID, Defender XDR, Sentinel, and Purview. This senior, hands-on role blends architecture and engineering to secure cloud, data, endpoints, apps and networks while enabling AI adoption.

You will lead security reviews, threat modelling and automation using Python, PowerShell, and Azure Functions; drive ISO 27001 and Cyber Essentials

Qualifications

• Hands-on experience in a Microsoft-centric security environment.
• Experience designing and implementing security controls across Microsoft 365, Azure and related tools.
• Ability to perform threat modelling and lead architecture reviews.

Responsibilities

• Design and implement security architecture across Microsoft 365, Azure, Entra ID, Defender XDR, Sentinel and Purview.
• Build modern security controls around Zero Trust, secure-by-design and automation.
• Lead architecture reviews and threat modelling for major projects and new technologies.
• Drive secure adoption of Microsoft 365 Copilot, AI agents and custom AI applications.
• Improve security monitoring, detection engineering and incident response.
• Support complex security incidents with internal teams and SOC partners.
• Strengthen vulnerability management using threat intelligence and risk.
• Automate security processes using Python, PowerShell, Logic Apps, Azure Functions and APIs.
• Provide evidence for ISO 27001 and Cyber Essentials Plus.

Skills

Threat modelling

Security architecture

Stakeholder communication

Security automation

Tools

Defender XDR

Sentinel

Entra ID

Azure

Microsoft 365

Purview

PowerShell

Python

Logic Apps

Azure Functions

APIs

Job description

Cyber Security Architect & Engineering Lead

Hybrid / Remote: Just 1 day per month in the London office

Leading UK Professional Services Firm

Ready to take the technical lead on security?

We're working with a leading UK professional services firm that is making a significant investment in its internal cyber security capability.

They're looking for a Cyber Security Architect & Engineering Lead to play a key role in shaping the firm's future security architecture and engineering capability.

This is a senior, hands-on position where you'll have the opportunity to design, build and improve security, rather than simply advise on it. You'll work across cloud, identity, data, endpoints, applications and networks, while also helping the business securely adopt AI and emerging technologies.

What You'll Be Doing

You'll take technical ownership across a broad security landscape, including:

• Designing and implementing security architecture across Microsoft 365, Azure, Entra ID, Defender XDR, Sentinel and Purview
• Building modern security controls around Zero Trust, secure-by-design and automation
• Leading architecture reviews and threat modelling for major projects and new technologies
• Taking a lead role in the secure adoption of Microsoft 365 Copilot, AI agents and custom AI applications
• Improving security monitoring, detection engineering and incident response
• Supporting complex and high‑severity security incidents alongside internal teams and external SOC partners
• Strengthening vulnerability and exposure management using threat intelligence, exploitability and business risk
• Automating security processes using Python, PowerShell, Logic Apps, Azure Functions and APIs
• Supporting technical controls and evidence for ISO 27001 and Cyber Essentials Plus
• Acting as a senior security SME and helping technology teams adopt better security engineering practices

What We're Looking For

This would suit an experienced Security Engineer, Security Architect or senior technical security professional who wants genuine ownership and influence.

Ideally, you'll bring:

• Strong hands-on experience within a Microsoft-centric security environment
• Excellent knowledge of Defender XDR, Sentinel, Entra ID, Azure, Microsoft 365 and Purview
• Experience designing and implementing security controls, not just recommending them
• Strong knowledge across identity, cloud, endpoint, data, network and application security
• Experience with threat modelling and security architecture reviews
• Exposure to detection engineering, incident response, threat hunting and vulnerability management
• Security automation or scripting experience
• Knowledge of Zero Trust, ISO 27001, Cyber Essentials Plus and NIST CSF
• The ability to communicate technical security risk clearly to senior stakeholders
• Experience within professional services, financial services or another regulated/client-confidential environment would be particularly useful.

One of the most interesting parts of this role is the firm's investment in AI.

You'll help define how technologies such as Microsoft 365 Copilot, AI agents and custom AI applications can be adopted securely, putting practical controls around identity, access, data and emerging security risks.

It's a great opportunity for someone who wants to build experience at the intersection of Security Engineering, Architecture and AI Security.