The Constitutional Court's ruling has cleared the way for Deputy Agriculture and Cooperatives Minister Thamanat Prompow but cast enormous doubts over his boss Prime Minister Gen Prayut Chan-o-cha.
The court last week deemed Capt Thamanat fit to serve as an MP and minister despite him being sentenced to four years in prison by an Australian court in a heroin smuggling case in 1993.
The Thai charter bars any person sentenced to a jail term from serving as a minister.
In Capt Thamanat's case, the charter court ruled that a jail sentence which could lead to his being disqualified as an MP and cabinet member must be handed down by a court in Thailand, not a foreign one.
It's rather ironic but now that Capt Thamanat has been officially whitewashed, the "dirt" seems to have been splattered all over his supporters.
The key point of the Constitutional Court's ruling is not just that Capt Thamanat is fit to serve but its acknowledgement that he was indeed sentenced by the New South Wales court for his role in trafficking to Australia 3.2kg of "high grade" heroin with a street value of $4.2 million at that time.
Capt Thamanat categorically denied this. Both during press briefings and in response to the opposition's censure motion in parliament, he insisted he "didn't import, produce or deal heroin".
Despite court documents obtained by The Sydney Morning Herald showing that he pleaded guilty and accepted a four-year jail term before being deported, Capt Thamanat told the media he denied the charge and was jailed for eight months under a plea bargain deal.
His response to the censure motion has since become infamous.
He said the substance the police and authorities in the state of NSW referred to as heroin was flour.
Capt Thamanat survived the censure debate with 269 votes of confidence from his party and coalition members. This should mean they trusted him and believed he was not a heroin smuggler. All he did was carry a few kilos of flour to Australia.
The Constitutional Court's ruling thus made for an awkward moment.
Now that the court said Capt Thamanat was indeed sentenced to a jail term by the NSW court in the heroin case, what to make of "plain flour" stories?
More importantly, how to deal with his criminal past? Since the constitution intends to put only decent people in ministerial positions, it not only bars those who have been sentenced to a jail term from serving but also those who have severely violated moral standards.
Would heroin trafficking fall into this category?
The onus falls on PM Gen Prayut. His options seem to be few and flawed, however.
Like other cabinet figures, the prime minister could focus only on the court's decision that the sentence handed down by the court in Australia had no legal binding in Thailand, continuing his support for the controversial minister. But that would leave a lot of questions about Capt Thamanat's criminal record and apparent lies.
His alleged heroin trafficking might be in the distant past, having occurred almost 30 years ago, but his attempts to cover it up are recent.
Gen Prayut's moral standards will definitely come into doubt. With Capt Thamanat's continued presence, the PM and his cabinet who often preach lofty values can only come across as a bunch of hypocrites.
The PM could choose to play innocent and say he was unaware of Capt Thamanat's criminal past before the court ruling but he would risk being seen as ignorant.
Capt Thamanat's life story is well-known and readily available in the mass media. Besides, each cabinet member must go through a thorough background check before being appointed.
If the PM plays dumb, he could be seen as, well, dumb.
Another option would be to say that the past is the past and every government has its flaws, like he has done before. This time, when a mere scandal has turned into facts in a court case, the chances are high that the PM would be seen as morally corrupt.
The PM could certainly choose the moral high ground and dump Capt Thamanat. But that does not seem to be an option.
Known as the government's fixer, Capt Thamanat said himself that he is the main artery supplying blood to the government's heart. If he falls, then the government will become unstable.
That would leave PM Gen Prayut with the unenviable choice of being seen as ignorant or suffering from moral bankruptcy. It's difficult to gauge which one would be better, or more fitting.
Atiya Achakulwisut is a Bangkok Post columnist.