Troops from other areas will be completely withdrawn from the restive southern border provinces by October, Prime Minister Prayut Chan-o-cha said.
Gen Prayut said he believes the unrest in the far South has improved over the past few years.
"I do not think Thai people want to fight each other. The situation is getting better, so troops [from other areas sent to the restive South] will be pulled out," Gen Prayut said.
The withdrawal process began last year.
The prime minister made a quick trip to Narathiwat on Monday to promote a land reform campaign in the deep South.
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Following the troop withdrawal, the Fourth Army will be responsible for the restive South backed by para-ranger forces in the area to promote peacekeeping and security operations.
Since 2007, 22 battalions from the First Army, responsible for the country's western and central provinces, Second Army, responsible for the northeastern quadrant, and Third Army, responsible for the North, have been sent to the far South to help the Fourth Army provide protection to locals on the order of then army chief Gen Anupong Paojinda.
However, nine para-ranger regiments have been established in the far South to accommodate the troop withdrawal.
The 15th Infantry Division was also set up in Pattani with the mission to help locals and develop the region.
Troops in the new division have undergone training to understand the needs of residents, the vast majority of whom are ethnic Malay Muslims.
Meanwhile, Gen Prayut will visit Malaysia on Aug 16 and will have bilateral talks with his counterpart Najib Razak on security issues, including the far South of Thailand.
