A 2015 audit by the International Civil Aviation Organisation (ICAO) of Thai airlines found "significant safety concerns" prompting the downgrade.
That triggered restrictions on Thai carriers launching new international routes, cramping expansion plans for a sector that has in recent years laboured under debts and management woes.
The removal of the red flag "shows the trust of ICAO and international community in Thai aviation," Prime Minister Prayut Chan-O-Cha told reporters on Monday.
Thailand received the all clear following a trip by ICAO officials to the kingdom in September, the Civil Aviation Authority of Thailand said in a statement.
More From This Section
"The lifting of 'red flag' status indicates that Thailand has dealt with the problems of under-standard of aviation safety," the CAAT said.
But "Thailand as well as CAAT need to carry on their missions to improve the aviation safety standards", it added.
ICAO had flagged several safety concerns including Thai aviation department personnel failing to meet international standards.
Prayut, who seized power in a 2014 coup, invoked special 'Section 44' powers to expedite safety improvements after the ICAO's warning.
Flag carrier Thai Airways has pulled several loss-making international routes while low-cost carrier Nok Air is struggling to make savings after years of losses.