Carlson Wagonlit Travel has bought Ark Travel, a Swedish independent agency.
It paid €30m (SEK273m) for 100% of the shares in the company which has offices in Stockholm, Gothenburg, Malmo and Gavle.
The take over is expected to be completed in December.
It has already been approved by the boards of the two companies.
It is the third privately-owned independent agency in Sweden to be bought by a larger TMC in the last six months.
BCD Travel bought Travelflow in May which doubled its size in the country.
MZ Travel was acquired in the summer by Ticket, a leisure group but which partners FCm Travel Solutions.
The Carlson move comes after its managing director in Sweden Marika Sharvik resigned and it later lost the TeliaSonera account, about 30% of its Swedish business, to HRG.
Cathrine Lundberg of CMM Consulting, a leading observer of Nordic business travel management, said: "Carlson was in urgent need of new leadership in Sweden and then they lost the TeliaSonera account so they had to do something.
"They have strong partners in Norway and Finland but they were too small in Sweden to make a difference.
"They will also have multi-national accounts in the Nordic region so they could not afford to be too small.”
But Ms Lundberg said the loss of mid-sized independent agencies in Sweden was becoming an issue.
"There are some companies which do not want to work with the very big agencies. A number of prime clients chose Ark because they were still a Swedish-owned independent company. This development could be a concern with their clients."
Jan Willem Dekker, CWT's executive vp for North Europe, said Ark was an established and successful business in Sweden with which CWT shared a common client.
"It represents a good fit with our external growth strategy," he said.