The firm has unveiled revenues of £2.2bn in 2018, up from £1.7bn in the previous year, while profits before tax rose by £10.3 million to reach £38.5m.
ISG said the results represent a third consecutive year of record-setting revenue and pre-tax profit figures, following its transition into private ownership three years earlier.
It also reported £1.4bn in forward orders.
Turnover at its UK construction arm climbed by £40m to £520m on the back of increased workloads secured through the public sector.
Meanwhile, the group said it overcame a challenging backdrop to double turnover in its European division to around £400m, which has seen “no discernible Brexit impact from its global customer base”.
Chief executive Paul Cossell said the firm was reaping the benefits of tackling “the productivity and cyclical financial issues” that have “plagued” the construction industry.
He added: “What’s clear is that ripping up the old rule book and learning from our tech-led customers has proved transformational for our business.
“Our people are already generating the ideas and innovation that are proving instrumental in moving forward.”