The Germany defender has approved a new three-and-a-half year contract while the veteran midfielder will sign for another year as Arsene Wenger also agrees an extension
The triple boost comes after the first-team duo joined Wenger and his backroom staff in agreeing to fresh terms with the club.
Wenger had agreed upon what is set to be a two-year contract extension last October, but an announcement on the manager's new agreement was delayed until Arsenal had secured the signings as a package.
Mertesacker, 29, has also approved a new three-and-a-half year contract that will tie him to the club until the summer of 2017, while Rosicky, 33, has agreed a new one-year rolling deal.
Sources have said that the new deals will be announced by Arsenal "within days", despite Rosicky having been linked with a potential switch to Bayern Munich in the summer.
Gunners chiefs had hoped to trumpet four new contracts but have failed to make a breakthrough in Bacary Sagna's long-running contract saga.
The Frenchman can leave on a free at the end of the season, and while Arsenal is still hopeful it can agree to new terms with the player, it has stepped up its search for a replacement by opening talks with Frankfurt for right back Sebastian Jung.
Members of Wenger’s backroom team have agreed to new contracts that will mirror those of the manager and keep them at Arsenal until 2016, with Wenger set to remain at the club for a 20th year, by which time he will be 66.
The fresh agreement will be on the same 7.5 million-pouds-a-year terms as his current contract. The club's longest-serving manager will not receive a pay raise, but the deal will be supplemented by incentives.
Mertesacker has 18 months remaining on his deal, but Arsenal was keen to reward his fine form this season with an extension.
Rosicky, whose current one-year deal runs out in the summer, will also remain at Emirates Stadium after agreeing a 12-month extension. Under the terms of his current contract, he was set to be offered fresh terms once he reached the 25-match landmark this season.
The Czech midfielder, currently sidelined with a broken nose, is the club's fourth longest-serving player after Nicklas Bendtner, Abou Diaby and Theo Walcott.