Belgium international centre-back Alderweireld, 24, leaves Ajax to sign a four-year contract at the Vicente Calderon, where he is joined by former St Etienne defensive midfielder Guilavogui.
The 22-year-old is a France international and commits his future to Atleti for the next five seasons, a statement published on the Spanish capital club's official website confirmed.
Alderweireld told clubatleticodemadrid.com: "I wanted to sign for one of the best clubs in Europe. I'm happy to be part of this club."
He had been linked with a move to Manchester City but instead takes the place of Martin Demichelis in the Atletico backline after the Argentinian decided to follow his former Malaga coach Manuel Pellegrini to the Premier League club on Sunday night.
The Belgian will reunite with countryman Thibaut Courtois - the Chelsea goalkeeper who is starting a third season on loan with the Primera Division outfit.
"He told me how great this team and its fans are," Alderweireld added. "He advised me to come because he is very happy here."
Guilavogui, who made 93 appearances for ASSE in Ligue 1, said: "I am pleased to join a big club like Atletico and am looking forward to playing in front of their fantastic fans.
"I hope to work hard for the team and win prizes in the coming years."
Atletico finished third in La Liga last season and director of sport Jose Luis Perez Caminero feels the defensive duo can provide extra security at the back while fellow summer signings David Villa and Leo Baptistao increase the side's goal threat.
He said: "Both players are strong, powerful and have quality. They will increase competition in the group and that will benefit everyone.
"They are young players with bright futures, but they have already competed at a high level for several seasons and will bring that quality into the squad."