Mainframe Solutions Architect - Contract

The Role

This opportunity is ideally suited to a senior Java/Mainframe Solutions Architect with deep experience in large-scale application transformation, legacy estate modernisation, and cloud migration programmes. Candidates should have a proven track record of guiding organisations through complex transitions from traditional platforms to modern cloud-native environments.

The assignment focuses on providing independent architectural oversight, technical assurance, and strategic direction throughout the migration of legacy business-critical applications into AWS-hosted solutions. The successful consultant will be expected to draw upon previous experience delivering comparable transformation initiatives and confidently engage with both technical and executive stakeholders.

Responsibilities:

• Assessing proposed modernisation and migration approaches to ensure they are practical, proven, and aligned with long-term architecture objectives.
• Reviewing cloud adoption strategies, application designs, and technology selections to validate suitability against operational, security, resilience, compliance, and business requirements.
• Highlighting architectural risks, dependencies, constraints, and design trade-offs, while recommending viable alternative approaches where appropriate.
• Evaluating commercial considerations associated with migration programmes, including software licensing, platform costs, tooling options, and third-party services.
• Producing recommendations, architecture assessments, and governance artefacts to support programme decision-making and investment cases.
• Analysing legacy application landscapes operating across hybrid and multi-cloud environments.
• Advising on application remediation, refactoring, and modernisation strategies for established Java-based platforms.

Knowledge Skills & Abilities

• Extensive experience in Java software engineering and enterprise application architecture.
• Delivery of large-scale legacy modernisation initiatives, including replatforming, refactoring, or cloud migration programmes.
• Strong AWS expertise, covering migration planning, architecture design, target-state definition, and cloud service selection.
• Experience working with complex legacy technology estates and long-lived application portfolios.
• Knowledge of software licensing, commercial modelling, and cost optimisation considerations within transformation programmes.
• The ability to challenge assumptions, provide independent architectural guidance, and communicate effectively with senior business and technical stakeholders.
• Experience operating within multi-cloud and hybrid-cloud environments.

Behaviours

• An open and genuine communicator
• Able to take responsibility for your actions
• Always learning and wanting to improve
• Takes responsibility for own development
• Love what you do
• Value and support your team
• Embrace who you are
• Open minded and willing to explore new ideas

What We Offer We value our team and to attract exceptional people, we offer an excellent package! In 2023, 2024 and 2025 we were recognised as one of the Best Workplaces in Tech by Great Place To Work UK, the global authority on workplace culture.
As a Leighton employee you can look forward to:

• A competitive salary this will be dependent on experience.
• A contributory pension scheme
• Private healthcare
• 25 days annual leave, plus bank holidays and the opportunity to buy or sell holiday
• A flexible approach to working hours
• Continuous personal development, career path and training
• And more....