The two division will operate as Ramboll Energy from January and will benefit from closer collaboration and synergies.
Ramboll said the shift in the world energy market towards a greener future means a new strategy is needed.
"Although oil and gas will continue to play a significant role in the energy mix in the coming years, there is a strong push towards renewables and a growing focus on sustainability. Large players in the oil and gas sector like Total and Statoil are changing their portfolio and strategies to accommodate for this green transition.
"Furthermore, the oil market has settled at a lower level after a drop in oil prices that is driving significant consolidation in the market," the company said in a statement.
The firm cited its recent move into the Chinese offshore wind market, where it provided foundation and substation design services to developer SPIC.
Ramboll said its energy division tackled the difficult seabed conditions, providing 100 steel monopiles. Meanwhile, its oil and gas division provided the design details for the 400MW project's substation.
"We already share a number of large energy clients. With our combined service we will have 1,500 employees dedicated to renewable and conventional energy locally and globally," said Ramboll Energy managing director Thomas Rand.