At the heart of our consultancy is Seán McCallion, a seasoned property development professional with over 25 years of experience delivering high-value, complex projects across Ireland and the UK. With a foundation in Quantity Surveying and a career dominated by senior roles at leading firms such as the Dandara Group Ltd., Barratt Homes plc, and Berkeley Group plc, Seán has built a reputation for excellence, innovation, and delivery.
At main board director level, Seán has overseen projects with individual values exceeding €150 million. His leadership has driven the successful completion of greenfield and brownfield residential schemes, mixed-use urban regeneration, commercial offices, and industrial/retail developments. Known for his strategic insight and hands-on approach, he excels in navigating the entire development lifecycle – from acquisition and planning to construction and disposal.
As the founder of ONLS, Seán now brings a wealth of expertise to private developers, funders, and stakeholders, providing sharp, independent guidance to ensure projects are delivered on time, within budget, and to the highest standards. His direction combines rigorous control systems, financial clarity, and the ability to build and direct high-performing multidisciplinary teams.
Our Mission
Our mission is simple: Deliver transformative developments with integrity, precision and commercial acumen.
Explore Our Projects
Discover the depth and diversity of our work across residential, commercial, and mixed-use developments. At ONLS Limited, each project reflects our commitment to strategic insight, meticulous delivery, and lasting value. From initial acquisition to final handover, our portfolio showcases the results of hands-on leadership and proven expertise.