Tony Cheng, who works for Chinese state broadcaster CCTV, was detained at Bangkok's Suvarnabhumi airport late last night under a law that has been heavily criticised by media groups.
Gas masks and ballistic vests are frequently used by reporters around the world but are classified as "war weapons" in Thailand and require a licence, something journalists have been unable to obtain.
"A British national was arrested and charged with illegal possession of war weapons last night at the airport," Suvarnabhumi airport policeman Somchart Maneerat told AFP today.
Cheng, who is married to a Thai national, and German colleague Florian Witulski were on their way to report from war-torn Mosul where troops are battling the Islamic State group.
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The pair previously reported from Mosul in March.
Witulski was briefly detained alongside Cheng but was later released and has not been charged.
Suvarnabhumi police said Cheng was released today afternoon after his wife paid a 100,000 baht ($3,000) bail and he agreed to forfeit his passport.
Media groups have repeatedly criticised the Thai law and say journalists should not be punished for carrying body armour and protective gear in and out of dangerous zones.
In a statement on Cheng's arrest, the Foreign Correspondents' Club of Thailand said reporters based in the country who travel to dangerous assignments are "presented with an invidious choice: break Thai law or increase the risk to life and limb".
Attempts over the years to amend the legislation have fallen on deaf ears, despite Thailand's own history of deadly street protests and a festering Muslim insurgency in the far south.
"The issue has occurred quite a few times already, I am certain there will be review on this matter," junta spokesman Major General Werachon Sukhonhapatipak told AFP.
He added that journalists should inform authorities if they plan to travel with such equipment.
Yet media groups have previously said that would not protect reporters from the risk of prosecution.
Bangkok has long been a regional hub for international reporters but since the coup the military have clamped down on dissent and made media visas harder to obtain.
A Thai court later quietly dropped the case.
During Thailand's regular bouts of deadly street protests, both demonstrators and journalists have donned ballistic vests and helmets, largely without falling foul of police.
Two foreign reporters were killed by gunfire while covering the worst round of political unrest in 2010.
"Both might have survived had they been wearing body armour," the FCCT statement said.