The 20-year-old, who made his first senior start for the Reds in the Europa League against Utrecht after six substitute appearances this campaign, trained with the League One side on Wednesday ahead of the paperwork being completed on Thursday afternoon.
Eccleston's loan spell is until May 31 and there is no recall clause in place.
"Happy and looking forward to the challenge at Charlton. With hard work the team is capable of achieving success," the player wrote on Twitter just after completing the formalities of the deal.
Source: PA
Source: PA