Gilchrist has signed on the dotted line for Sheffield United in the Championship.
The Blades, who were relegated last season, have secured the 20-year-old by promising him regular game time.
Manager Chris Wilder commented: "The loan market tends to be one which intensifies later in the window, so we accepted we would have to wait a little longer if we wanted our top targets. Alfie was always one of those players who featured high on our wanted list.
"Everyone in the game is aware of Alfie and his abilities, so our pitch to him, and Chelsea, had to be spot on. There's been a lot of work behind the scenes to get this deal through, and we're looking forward to working with a really talented player.
"Alfie's had a taste of playing at the highest level, and having spoken to him, he's keen to get more games under his belt. He's ready to take the next opportunity in his career and we're delighted to have added him to our squad."