The 22-year-old former Bournemouth frontman was in the stands to watch Albion's FA Cup win over Newcastle on Saturday and could make his debut in Tuesday's trip to derby rivals Crystal Palace.
"Sam is a traditional centre-forward, physically strong, and the type we feel will complement the strikers we have here," manager Gus Poyet told Brighton's official website.
"It's always difficult for a loan player but I hope we can be the club at which he flourishes, and that his style of play will suit the way we like to play.
"We have an opportunity to get to know each other between now and the end of the season."
Vokes has also had spells on loan with Bristol City, Sheffield United, Norwich, Leeds and Burnley.