Reaching way back in the memory banks to when I worked for an outdoor retailer.. There are two parts to this - cleaning the Gore-Tex membrane so that it doesn't have anything clogging the pores, and renewing the DWR on the outer shell.
DON'T use a normal liquid laundry detergent because it will interfere with the membrane. Find something specifically formulated for use with Gore-Tex (Nikwax Tech Wash, etc).
Once it's clean, then use something like TX Direct to restore the DWR coating on the shell fabric. If I remember, the spray-on version is supposed to work better than the wash-in because it's only getting applied to the outside of the jacket, but it's more of a PITA to apply evenly and completely.
^^^ This right here. Applies to Event fabrics as well. Appropriate washing keeps the membrane working; renewing the DWR helps as well.