Jonathan Head, the BBC's Southeast Asia correspondent, faces up to five years in jail at the private prosecution on the popular tourist island of Phuket.
Rights groups have said the case exposes how Thailand's broad defamation and computer crime laws scupper investigative journalism and make it difficult to uncover wrongdoing in an endemically corrupt country.
The prosecution was sparked by a 2015 report by Head detailing how two foreign retirees had Phuket properties stolen from them by a network of criminals and corrupt officials.
The man bringing the prosecution is Pratuan Thanarak, a local lawyer who featured in the BBC's report looking at how Rance lost USD 1.2 million worth of properties.
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According to the report, Pratuan admitted on tape to certifying Rance's signature without him being present, a move which helped the British retiree's then wife transfer his properties out of his name.
She was later convicted and jailed for the scam.
A copy of Pratuan's complaint seen by AFP alleges that the BBC's report caused him to be "defamed, insulted or hated". It does not detail whether he notarised the signature without Rance being present.
Neither Head nor Rance spoke to reporters on their way into the Phuket court today.
In a previous statement the BBC has said it "stands by its journalism" and that they "intend to clear the name of our correspondent".
Rance and Head face one charge of criminal defamation, which carries up to two years in jail.
Head faces an additional charge under Thailand's Computer Crimes Act, a broadly-worded law which forbids uploading "false data" online and carries a five-year maximum jail penalty.
Private citizens can also launch their own prosecutions and they are not forced to pay costs if they lose.
Similar cases have been brought in recent years.
Local news site Phuketwan closed down in 2015 after running out of money in its successful bid to defeat a suit brought by Thailand's navy.
Andrew Drummond, a British crime reporter, left the country the same year because of multiple cases brought by those he exposed as did British labour rights activist Andy Hall in 2016.
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