Fractional CTO for startups & scale-ups
I help founders give their product and engineering teams the direction they need to deliver more predictably, make better decisions, and build momentum with confidence.
30-minute introductory call. No preparation needed.
At critical points in a company’s journey, product and engineering teams can lose momentum: delivery becomes unpredictable, leaders need more senior direction, or the next hiring or technical decision feels unusually high-stakes.
I help founders turn those moments into a clear, practical plan - aligning customer needs, product priorities, team capability, risk, and commercial goals. The result is less friction for your team and more confidence in what happens next.
I adapt every engagement to your company’s decisions, pace, and internal capability. You may need clear advice, senior leadership inside the team, or hands-on support to turn a plan into progress.
I help you turn a promising opportunity into a focused first product that gets you learning from customers quickly.
I help you give your product and engineering teams the direction, habits, and leadership they need to deliver predictably.
I help growing companies keep delivery moving while building the trust and foundations customers expect.
Drawing on my experience co-founding an AI-first business, I help you find practical AI opportunities, test them quickly, and build what creates durable customer value.
For more than two decades, I have built products and led technology teams in founding CTO roles, venture-studio leadership, and enterprise AI delivery.
I co-founded and led technology for an enterprise AI platform, taking it from early idea to enterprise pilots and commercial deployments. I led the ISO/IEC 27001 certification work and built the privacy, security, and deployment options needed to earn enterprise confidence.
At a financial-wellbeing platform, I built the initial product and technology function, including products that connected with regulated providers. The business expanded to three countries within 12 months, and I hired the senior team to take the function forward.
As Group CTO at Forward Partners, I worked with more than 70 portfolio companies - from pre-seed through Series A. I helped founders make critical product and technology decisions, build early teams, hire well, and prepare for the next stage of growth.
I have built products and engineering teams across AI, B2B SaaS, data, e-commerce, marketplaces, mobile, games, and education - helping companies move from a first product to international expansion and commercial delivery.
I believe technology leadership is most valuable when it creates momentum rather than another layer of process. I combine executive-level judgement with enough involvement to make decisions real.
I start with your commercial objective, customer context, product, and team - not a preferred solution. Together, we identify the few decisions that will have the greatest impact.
I turn priorities into a clear technology and delivery plan: what to build, what to defer, who needs to own what, and how progress will be measured.
I work with founders and teams to resolve architecture, product, hiring, delivery, security, and vendor decisions quickly. I stay close enough to the work to remove blockers directly.
My goal is not long-term dependency. It is a more capable team, a clearer operating model, and a technical foundation that supports your next phase.
I’m Leonidas Tsementzis, a founder, technology executive, and hands-on CTO based in London. For more than 20 years, I have built software products, led engineering teams, and helped founders make the technology decisions that define what their companies can become.
My career includes founding and co-founding companies, serving as Group CTO for an early-stage technology investor, and working with venture-backed teams across the UK and Europe. I have built initial products, recruited teams, shaped technology strategy, led enterprise security and compliance work, and handed over stronger technology functions to permanent leadership.
I am particularly energised by ambitious startup and scale-up problems: finding product-market fit, turning a complex idea into a product customers can trust, using AI responsibly, and building the systems and teams that turn early momentum into durable growth.
I tailor every engagement to your stage and the problem in front of you. Some teams need a strategic assessment and a clear roadmap; others need embedded leadership over several months. I shape the work around the decisions, delivery rhythm, and hands-on support that will make the biggest difference.
I am most useful when technology is central to your business, but a permanent CTO hire is premature or the role is still taking shape. I can also help during a transition, a new product build, a scale-up phase, or when you need to build customer confidence.
Yes. I work to strengthen the team already in place by clarifying priorities, improving delivery, coaching leaders, helping with hiring, and resolving difficult technical or organisational decisions.
Yes. I focus on AI products and capabilities that create customer value, can be evaluated properly, and are appropriate for your risk profile. I can support discovery, the foundations behind the product, implementation, and getting it ready for customers.
Yes. I am based in London and work with teams remotely, with in-person time where it materially improves the engagement.
Let’s start with a conversation
If you are building a startup, preparing a scale-up for its next chapter, or need experienced technology leadership for a critical moment, I would be glad to talk.
Book an introductory callPrefer email? Use leo@lightwatch.io.
I'm based in London but I partner with ambitious teams worldwide.