The Thailand international will play for Almeria on loan from July this year to July next year with an option for the La Liga club to buy the forward.
''I am very happy and would like to thank all concerned parties for their support for me to play in Spain,'' said Teerasil.
''I hope this will lead to other Thai players getting chances to play in Europe. I think I will not have problems playing in Spain.''
Teerasil trained with La Liga side Atletico Madrid last year after an unsuccessful spell with Manchester City several years ago when the English club was owned by former prime minister Thaksin Shinawatra.
The contract was signed at SCG Muang Thong Stadium and Teerasil is expected to receive around 900,000 baht a month.
Almeria vice president Jose Juan Medina said the deal was important for both Thai football and Almeria.
''We hope that Teerasil will become a successful player with Almeria,'' he said.
Almeria sports director Alberto Benito said: ''Many people may ask if Teerasil is good enough to play for Almeria or not, and I think he is. We have watched tapes of him playing and his style suits La Liga. He can play in every attacking position.''
Teerasil will become the first Thai to play in the Spanish top flight - if Almeria avoid the drop at the end of this season.
Almeria are currently fifth from last in the 20-team La Liga, four points above the relegation zone.