QPR have signed Swindon Town midfielder Massimo Luongo, who is set to be followed to Loftus Road by Ben Gladwin.
Teenager Mark O'Hara has signed a two-year extension with Kilmarnock.
Szczesny has established himself as Arsene Wenger's first choice in goal this season, taking on the momentum from the end of 2012/13 when he finished strongly with four clean sheets in six games.
His form has continued this season and he has been a mainstay in Arsenal's Premier League-leading side.
The 23-year-old joined Arsenal's academy from Legia Warsaw in 2006 and made his first-team debut in 2009, going on to pass the century of senior appearances last season.
Szczesny told the club's official website: "I am very pleased to have signed a new contract. Arsenal is like my family and I'm so happy to be committing my long-term future here.
"I've been at this club for over seven years now and I'd just like to take the opportunity to thank everyone for their support towards me during my time here.
"Many people have given me amazing support since I arrived as a boy, people like Tony Roberts, who helped my development as a player from a young age. I'm so proud to be an Arsenal player and am looking forward to helping our club towards success in the years to come."
Wenger added: "We're very pleased Wojciech has signed a new long-term contract. I have always believed he is an extremely talented player, with excellent reflexes and good mental strength.
"He continues to grow and improve all the time too, so he has the potential to be even better. He can be an important part of Arsenal Football Club for many years to come."