The scrum-half has spent the entirety of his career with the Mattioli Woods Welford Road outfit, and at the time of writing has amassed an eye-watering 332 appearances for the club.
He is also England's most capped player with 127 caps.
Youngs is also one of the most decorated players in English rugby history, with five Premiership titles and three Anglo-Welsh Cups to his name.
He has also represented England at four World Cups, toured with the British and Irish Lions in 2013 and played for the Barbarians.
"It's a bittersweet feeling really," Youngs said on his retirement. "Obviously, I'm sad at the thought it's coming to an end but I'm excited about the rest of this season, excited about what this group can do.
"That's the strange part, I'm using the 'r' word (retirement) but it isn't over today, there is still plenty of rugby left this season and that's what is at the front of my mind. I'm not done, let's not write the obituary just yet.
"I have spent two decades of my life here at the club and I have been lucky to be a part of some incredible moments along the way, enjoyed so much success and made memories that will last a lifetime.
"It's all I have known in club rugby, the green, red and white, and all I've wanted to know. The idea of playing against this club wasn't ever an option for me and so, for me to be able to finish a one-club player will be one of my greatest achievements.
"The time will come to thank everybody who have helped me achieve what I have but, that's for when it comes to an end. For now, it's about finishing this chapter of my life with some more success. I'm not done just yet."
Youngs also represented the Tigers alongside brother Tom before the hooker retired in 2022.
Leicester currently sit in second position in the Premiership standings with just four rounds of the regular-season remaining.
Liam Dawson is set to play his first T20I for almost three years after being selected in England's squad for the white-ball series against West Indies that starts later this month.
Arsenal's push for a strong Premier League finish has taken a significant hit, with manager Mikel Arteta admitting Declan Rice's injury "does not look good" following his absence in Sunday's intense 2-2 draw with Liverpool at Anfield.
Virat Kohli has informed the Board of Control for Cricket in India (BCCI) that he is considering retirement from Test cricket ahead of India's crucial red-ball tour of England starting in June.
The DR Congo senior men's national team has received a major boost with the inclusion of West Ham United defender Aaron Wan-Bissaka, who has officially switched his international allegiance to represent the African nation.
