The O’s central midfielder has moved to Roots Hall on loan until the start of January ahead of Saturday’s match with York City.
Laird began his career with Manchester City before spending time on loan with borth Northampton Town and Port Vale.
He then joined Millwall in January 2008 and made 92 appearances for the Lions.
Loan spells with Brentford and Walsall followed before the 26-year-old joined Leyton Orient in July 2011.
He has since made 29 appearances for the O's but just two of those have come this season and he is keen to be playing regular first team football.
Manager Paul Sturrock told the official website: “Marc will add something that we are lacking in the middle of the park.
“He’s a good passer and he will add some strength and experience there.
“We still probably need another player in there and hopefully we can make that happen next week now.”
Orient have given the club permission for Laird to play in the FA Cup however the midfielder is already cup tied in the Johnstone’s Paint Trophy having played for the League One side.