The group reported a pre-tax profit of £4.3m last year, having suffered its first-ever loss in 2018 of £6.4m.
Revenue at R G Carter, which employs around 1,100 people, jumped by 18% to £317m.
Despite disruption in the first lockdown, chairman Robert Carter said the business enjoyed significant cash reserves of £66m with no external borrowing.
He said: “In the construction division, we completed some exceptional projects for our clients. I am pleased to return to profitability, as this allows for innovation and investment in the future.
“We are well-placed to undertake future opportunities but there will inevitably be further challenges.”
R G Carter will celebrate 100 years in business next year.