Paton, 30, who has made five appearances for Northern Ireland, was released by St Johnstone in January and has joined the Pilgrims as a free agent.
‘Paul joins Argyle to bolster manager Derek Adams’ midfield options, and he goes into the squad for Saturday’s home fixture against Bristol Rovers,’ the Sky Bet League One club said on their official website.
The transfer is subject to the usual necessary paperwork being completed.
Paton began his career at Queen’s Park and he had also had spells atPartick Thistle and Dundee United before moving on toSt Johnstone, where he made 55 appearances.
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.