The 26-year-old spent the first half of the season on loan at Vitesse Arnhem but his time was hindered by injury.
On the loan signing, Garner said, “Jamal is a very talented goalkeeper and I'm delighted to welcome him to the football club.
“Jamal is someone who I actually tried to sign as a youngster at Crystal Palace, as his talent and ability was evident at an early age.
“He's had a good upbringing at Chelsea and has benefited from a number of different loan spells throughout his career.
“The owners and recruitment team were very supportive in getting this deal done & it is a credit to the structures that we have in place that we've been able to secure what we think is a good deal for the football club.
“We would like to thank Chelsea for the swift nature in which the deal was concluded and I'm looking forward to working with Jamal for the remainder of the season."