The 21-year-old winger made eight senior appearances for Palace last season in all competitions, building on a strong loan spell at Charlton Athletic the previous year, when he scored 15 times and registered nine assists in 49 games and earned an EFL Young Player of the Season nomination.
Rak-Sakyi will be looking to help Sheffield United make an immediate return to the Premier League in 2024/25, following their relegation to the second-tier last season.
The club wishes Jes the best of luck for his loan spell at Bramall Lane.