The US-based company is not currently conducting an external search for Garratt's replacement, it said in a statement, citing its 'robust succession plans'.
Garratt's retirement comes at a time when retailers are facing a shift in consumer spending patterns, as penny-pinched Americans cut back on discretionary items and trade down to cheaper alternatives such as dollar stores for grocery needs.
Annual Profit Forecast
While that has helped boost sales at Dollar General, the company in December trimmed its annual profit forecast, as cost pressures tied to its supply chain problems continued to squeeze its margins.
Garratt, who joined the company in 2014 and was named the CFO a year later, said "while I look forward to spending more time with family, this was a difficult personal decision."
"The timing of the announcement with John assuming the President title just six months ago does strike us as a bit unusual, but we don't think there is anything more to read into the news," said Gordon Haskett analyst Chuck Grom.
Read More: Dollar General Opens Its 19,000th Store
The Tennessee-based retailer in July last year named Jeff Owen its chief executive, replacing Todd Vasos, who stepped down in November to take on an advisory role until April. Vasos is set to retire from the business after that.
Last week, rival Dollar Tree Inc said Executive Chairman Richard Dreiling, would replace Chief Executive Officer Mike Witynski, nearly a year after its settlement with an activist investor. Dreiling has previously served as chairman and CEO of Dollar General.