Scrum half Deacon and back rower Morrison are out injured, so Lynch will step in for the games against Leeds and Wakefield.
Lynch, 29, joined the Bulls in 2005 from Castleford Tigers and has made 127 appearances for the club.
He said: “I am honoured and delighted to have been chosen to Captain the Bulls. It’s disappointing that we have both Paul and Glenn out injured but we have a great squad with a wonderful spirit and I am confident we will perform to the highest order over the next few games.”
Coach Steve McNamara had no hesitation in turning to Lynch for the busy Easter schedule. He said: “Andy is an outstanding leader for us with his actions both on and off the field and he will do a tremendous job in the role as Captain.”