The literary contest, which is sponsored by Bangkok Bank and Praphansarn Publishing House Co, is in its second year.
Ms Thanadda's biographical work Chan Chue Eri: Kap Prasopkarn Tang Daen (I Am Eri: My Experience Overseas) was selected as the winner from 13 entries this year.
She said the book was based on her personal experience after she was lured into work as a prostitute.
She said she was born into a poor family and had to struggle to make ends meet during her childhood.
An unplanned pregnancy as a teenager meant she had to drop out of school. As a result, her family and others who were close to her decided to turn their backs on her.
Ms Thanadda said she was first lured into prostitution in Pattaya before travelling to work as a sex worker in Hong Kong and Japan, where she suffered mistreatment. She was involved in drug abuse and gambling and was sent to jail for possession of psychotropic substances.
"I wanted to reveal the life of a woman who hopes to make a fortune from such a career to escape poverty," she said.
"But she steps into a [vicious] cycle only to suffer the mental and physical traumas that lie in wait.
"I want to share these experiences so they can be a lesson for those who want to take the wrong path."
Ms Thanadda said she was not that concerned about the prize money she would receive but she would be happy if she found out that her experiences proved useful to other people.
She said she gained recognition from other inmates during her three years in jail. She offered to write appeals for them to have their convictions overturned.
Thanks to her assistance, many of them had their sentences reduced and, in some cases, court rulings were reversed and they were set free from prison, Ms Thanadda said.
She said she has now turned her back on prostitution and is hoping to become a make-up artist.
She said her boyfriend, an American named Dave, inspired her to pen the book. The man has done all he can to find ways to help pull her out of prostitution, she said.
Phra Paisan Visalo, a member of the judging panel, said the book reflected the deeply entrenched problem of prostitution facing Thai society.
The panel of judges decided to pick Ms Thanadda's work as the winner because her approach was unusual and refreshingly different in that she tells the story from her first-hand, personal experience.
Many other authors who pen similar books revolving around prostitution only related their story from the angle of an observer, Phra Paisan said.
Sakchai Chirathivat, an executive of Praphansarn Publishing House Co, said that modern non-fiction was the theme of this year's contest whereas last year's contest focused on fiction.
Ms Thanadda will receive 50,000 baht in cash and a diamond brooch for winning the contest. The work will be published into pocketbooks in Thai and English.