Overall revenue growth across the year at the Paris-based holding company, which owns a number of Havas-branded marcoms agencies as well as Arena Media, Forward Media and others, was 17.3 per cent and operating margins grew 30 basis points to 14.4 per cent.
Organic revenue growth across the year was 4.7 per cent in Europe and 6.4 per cent in North America, with Asia Pacific up seven per cent and Latin America up 1.3 per cent. However, Q4 organic revenue growth globally was 3.1 per cent, against 5.5 per cent in Q3.
Havas commended the "outstanding" performance of France in Q4, when organic revenue grew 6.6 per cent, up from 0.6 per cent in Q3, leaving growth of 3.2 per cent across the year.
In the UK, organic revenue grew 4.4 per cent to reach €286m (£226m, $316m), although growth was just 1.6 per cent in Q4.
There was a similar picture in other European countries, where organic growth in Q4 was 4.5 per cent against 7.3 per cent in Q3; Havas said there was double-digit growth across the year in Spain, Germany, Italy, the Czech Republic, Switzerland, Hungary and Ireland.
The Q4 dip was most pronounced in North America, where organic growth was one per cent, against 7.3 per cent in Q3. Full-year revenue in that region was €777m (£614m, $859m).
Havas said full-year growth in North America was driven by Havas Life, Arnold, Havas Edge and Havas Chicago "on the strength of the many new business wins of 2014".
Havas said APAC "remains very dynamic thanks to high levels of new business over the past two years". Organic growth there accelerated from 8.1 per cent in Q3 to 8.3 per cent in the fourth quarter. The main contributors were Australia, the United Arab Emirates, the Philippines, Indonesia and South Korea, the firm stated.
Latin America returned to growth in Q4, with organic revenue up 0.2 per cent against a decline of 0.9 per cent in the third quarter. "Both Brazil and Argentina produced sound performances," said Havas.
The company did not provide specific details on the performance of its PR business, which includes Maitland, Cake and Havas PR.
Overall revenue growth followed a series of acquisitions, including London-based health comms agency Just:: Health and German PR firm Bird & Schulte.
The net value of new business wins in 2015 totalled €1.69bn (£1.33bn, $1.87bn).
Havas CEO Yannick Bolloré said 2015 was "another record year for the group".
He said: "These results are the outcome of a highly effective strategy centred on collaboration and integration among all the group's areas of expertise, to provide our clients with an efficient and innovative service that seamlessly combines creative, media and digital.
"These excellent figures give us every reason to start the year with confidence; they must also motivate us to redouble our efforts to ensure the quality and innovation of our offerings."
The company said it had now expanded its Havas Village concept, which sees multiple brands housed in one space, to 37 sites worldwide. Ten opened in 2015, with London and Barcelona among those planned to open this year.