Time has been called on the five-year-old's career after she struggled for fitness since she finished last in the Gold Cup at Royal Ascot in June.
Simple Verse was initially disqualified and placed second behind Bondi Beach in the Leger two years ago but she was reinstated as the winner upon appeal.
The daughter of Duke Of Marmalade then claimed the only other Group One triumph of her career when she won the British Champions Fillies & Mares Stakes at Ascot a month later.
A statement posted on www.rbeckett.com read: "It has been decided to retire Simple Verse.
"She has had various issues since the Gold Cup in June, and put simply we have ran out of time to get her ready for the Long Distance Cup, on Champions Day.
"She was a terrific servant to all her connections. The highlight of her career was undoubtedly the 2015 St Leger, but to drop back to a mile and a half and win the Fillies and Mares five weeks later showed how versatile, as well as tough and talented she really was.
"We will miss her, but look forward to training her progeny."
Simple Verse, owned by Qatar Racing, won six times from 15 starts and earned over £965,000 in prize-money.