The 20-year-old defender broke into the first team last season, but this year has appeared as a substitute in the Europa League.
Medley, who joined Chelsea as a child in 2016, a regular under-23 who finished sixth in Premier League Two but is now advancing.
The former 6-foot-5-inch former young star of England will spend 12 months at Priestfield Stadium after the Gills rejected several clubs for signing.
Announcing the on his website, director Steve Evans said: “We are very pleased that Zech joins us.
“The boy has taken his time, has spoken to many clubs and is a very good addition.
“I would like to congratulate Mikel Arteta and his Arsenal team for agreeing to allow Zech to continue his studies here.
“He’s a boy from Medway, he went to school in Gillingham and his circle of relatives still lives here, in many tactics is one of us.
Arsenal desperately needs back reinforcements and is fighting Manchester United for 27 million pound Lille star Gabriel Magalhaes.
Calum Chambers may be on the brink of extinction, with Fulham lining up a bid of 12 million pounds for the defender.
Arsenal has won the primaries in their quest for a midfielder after Lyon sporting director Juninho admitted that Houssem Aouar could leave this summer.
Arteta could also play Lucas Torreira for Amadou Diawara of AS Roma.
It would provide a budget option of Thomas Partey’s long-standing goal, which will charge them at least forty-five million pounds and 200,000 pounds a week in salaries.
© News Group Newspapers Limited in England No. 679215 Headquarters: 1 London Bridge Street, London, SE1 9GF. “The Sun”, “Sun”, “Sun Online” are registered trademarks or industrial names of News Group Newspapers Limited. This service is provided under the popular terms and situations of News Group Newspapers ‘Limited, in accordance with our privacy and cookie policy. For information about a hardware replica license, visit our distribution site. Check out our online press kit. For any additional requests, please contact us. To view all the contents of The Sun, use the site map. Sun’s online page is regulated through the Independent Press Standards Organization (IPSO)
Our hounds aspire to precision, but we make mistakes. To learn more about our claims policy and to file a claim, click here.