The Royal Forest Department and the Department of National Parks, Wildlife and Plant Conservation are expected to merge within a year, after senators on Tuesday passed a motion to support the move.
Manophat Huamuangkaew, director-general of the Parks Department, said the bill will now be sent back to the House for consideration as the Senate amended some of its details.
If the House agrees to the changes, the bill will be forwarded to Prime Minister Yingluck Shinawatra who will seek royal endorsement.
If the House disagrees, a joint committee from the Senate and the House will make a final decision.
The merger plan will take effect once the law is announced in the Royal Gazette.
"We expect to complete the whole process in a year," Mr Manophat said.
The merger will allow for better management of natural resources protection as there will be no overlap between the two departments, he said.
While the merger might result in some restructuring to improve management, employees of the two departments need not worry about losing their jobs, Mr Manophat said.
"I am not worried about a lack of management positions after the merger as a number of officials are planning to retire in October," he said.
The Forest Department will resurrect the positions of regional forest head, provincial forest head and district forest head, he said.
Boonchob Sutthamanuswong, chief of the Forest Department, said this is the third attempt to merge the two departments.
The first was in 2005, but was halted due to the military coup in 2006. The second was made during the tenure of natural resources and environment minister Suwit Khunkitti, but failed due to the dissolution of parliament in 2011.
This latest attempt at a merger was driven last year by Natural Resources and Environment Minister Preecha Rengsomboonsuk.
The Department of National Parks, Wildlife and Plant Conservation was separated from the Forest Department in 2002 in a move led by Deputy Prime Minister Plodprasop Suraswadi, who was then permanent secretary for natural resources and environment.
The decision was taken to improve the management of workloads.
Mr Plodprasop was the department's first director-general.