A more cautious approach to risk saw revenue fall by just over a third to £297m in the year to December 2023.
But operating margin rose to 3.3% from 1.5% previously as pre-tax profit jumped by almost half to £9.9m.
Headcount at the the Gerrards Cross-headquartered business remained stable at around 200 staff.
Jackie Wild, Founder and CEO of TSL, said: “Despite a challenging year for the construction sector, with many high profile insolvencies, TSL’s results show a strong and resilient performance.
“The group made a strategic decision to focus on securing projects which could deliver sustainable levels of contribution, enabling us ot improve gross profit margin from 3.1% in 2022 to 5.5% in 2023.”
She added that TSL had secured a strong pipeline of projects for 2024 on a negotiated basis, reducing the impact of price volatility, with 92% of work already confirmed.
After a year of further expansion under the Tonroe Group, the firm expanded its operations in Europe strengthening its presence in Ireland, Germany and securing first work in the Netherlands and Spain.
It also expanded in Canada and is in the process of restructuring its UK and international businesses into a new group holding structure, which will be registered in the UK.
Wild said: “This process will be completed by August and will set the trajectory for TSLs’ International growth strategy.”