Having made his debut as a 19-year-old off the bench against Ulster in March 2009, Horne's versatility and game intelligence quickly made him an integral member of the Glasgow setup.
He earned an awards double at the end of 2012/13, taking home the club's Try of the Season award for his memorable score against Northampton Saints at Scotstoun whilst also being voted as the Players' Player of the Season.
Part of the club's history-making title-winning season in 2014/15, the centre was named to the Guinness PRO12 Dream Team after a campaign that included a scintillating hat-trick against Cardiff Blues at Scotstoun.
Together with brother George, Horne holds the record for most matches in which siblings have scored; the pair have touched down in the same match on five separate occasions, including the 2019 Guinness PRO14 semi-final victory over Ulster and, most recently, against Benetton in January 2020.
His work ethic and form earned Horne selection for two Rugby World Cups - in 2015 and 2019 - as well as making him a regular under both Vern Cotter and Gregor Townsend, earning 45 caps in a Scotland jersey.
Alongside the Fagerson brothers, the Hornes are the most recent set of brothers to start a Test for Scotland, having become the 49th set of siblings to pull on the dark blue jersey back in 2018.
"I feel incredibly fortunate to be retiring on my own terms, after a career with both Glasgow and Scotland that I'm immensely proud of," said Horne.
"Having spent many years playing under some of the very best coaches in the game, I have been inspired to follow in their footsteps and make the move into coaching myself.
"I know I'm so very lucky to have experienced all that I have, and to have done so playing alongside my childhood best friend and my little brother has been a dream come true. I have relished every moment of my 13 years and look back on it with only the happiest of memories and great pride.
"Thank you to all who have supported me on my journey so far - I will forever be grateful to each and every one of you. Here's to the next chapter!"
Glasgow Warriors Managing Director Al Kellock paid tribute to the club centurion, saying: "Pete's journey through rugby has been an inspirational one - from winning the Schools Cup with Bell Baxter and his time at Howe of Fife, to all of the memorable moments he's had in both a Glasgow and a Scotland shirt, his standards have never wavered from wanting to be the best.
"For any young kid growing up and wanting to play rugby, Pete is a perfect example of how to approach your rugby and how far you can go.
"He's been a phenomenal team-mate and a phenomenal friend to so many at Glasgow Warriors. I've had the privilege of playing with him and also seeing the influence he has had on shaping the club as it is today. He's a first-class professional that takes a huge amount of pride in making sure he is exactly where he needs to be.
"Pete undoubtedly has a tremendously bright future ahead of him, and we look forward to seeing how he develops as a coach at Ayrshire Bulls; he's someone that will always remain close to the heart of this club."
Glasgow Warriors Head Coach Danny Wilson added: "Having made over 180 appearances for Glasgow in 12 years at the club and representing his country, Pete has achieved a huge amount in the game.
"It's rare in the modern game that a player spends their whole career at one club and Pete's passion and commitment to Glasgow Warriors should be celebrated.
"He's been a key part of our leadership group for a number of years and will be missed by all at the club.
"His attention to detail in his preparation both on and off the pitch is outstanding and recently his work mentoring our younger players and helping ensure the team taking the field are fully prepared has been fantastic.
"Pete has been a great servant to this club and we wish him, his wife Kirsten and their children all the best for the future."