The 22-year-old, who began his career at Sporting Fingal, will be available after January 2.
Dawson, who has represented the Republic of Ireland at Under-15, Under-16 and Under-18 level, boosts manager Gary Johnson's options after a number of loanees returned to their parent clubs.
Dawson told the club's official website: "I am over the moon to sign for Yeovil Town.
"I am friendly with Paddy Madden, who has only good things to say about the club. I am really looking forward to playing in green and white."