Government spokesperson Traisuree Taisaranakul said the Cabinet had agreed to give Thanaphon Siwirat, a former beauty queen, a position in the office effective from Tuesday.
Sirawat has frequently been spotted accompanying Thammanat on his official duties.
The move has once again sparked allegations of nepotism in government, especially from pro-democracy netizens.
Thammanat has managed to keep his job as deputy agriculture minister despite records that show he served four years in an Australian jail for heroin smuggling in the 1990s. His case has prompted questions about the transparency of Prayut Chan-o-cha’s government.