Nelson will be with the Blue and Gold until the end of the 2016 season, while McPherson will join the club in the 2015 season on a train and trial basis.
"Cody's a talented back-rower, and Shannan is both experienced and hard-working, so they will be great additions to the forwards in our squad," Eels Head Coach Brad Arthur said.
"I'm looking forward to working with them both when the 2015 pre-season comes around."
25-year-old Nelson made his NRL debut with the Titans earlier this season, while 28-year-old McPherson will return to the NRL after a two year stint in UK Super League.
"I'm proud of what Brad and his squad have achieved this year, and our new recruits are part of the next stage of continuing the improvement at Parramatta," Eels CEO Scott Seward said.Like