The new series will begin airing on Sky One on Wednesdays from the 22nd July, with all episodes available on demand from that date.
The new series will also see Walter's mum appear for the first time. Played by Ellen Thomas, the character has to date only been heard on the telephone.
Producers explain: "The third series of this semi-autobiographical Sky One comedy, loosely based on Idris's own childhood, sees the welcome arrival of Walter's mum from Sierra Leone with Walter desperate to impress.
"Bagpipes has a near death experience that makes him question the meaning of life. Valentine finally finds love and Kirsty sets up her own catering business all while Agnes gets suspicious as some developers start taking an interest in the Eastbridge Estate, threatening the very existence of the community."
Idris Elba says: "Nothing beats a funny story from someone who was there! I can't wait for viewers to see Series 3."
Sky's Jon Mountague comments: "Our chests are puffed out with pride for the return of Idris Elba's award-winning In The Long Run. Chapter 3 has more LOLs than ever and as we've come to expect, is shot through with family, community and togetherness."