Sendles-White was released by Swindon in May after making 17 appearances.
The 23-year-old, capped 12 times by Northern Ireland at under-21 level, started his career at QPR and has also had spells with Hamilton and Mansfield.
Dayton, 28, most recently played for Cheltenham Town, where he turned out 36 times for the club last season.
Leyton Orient have signed defender Jamie Sendles-White on a one-year deal and midfielder James Dayton on a two-year contract.