Drummond is to appear as agency nurse Chantelle Lane, who is brought into the hospital by Sacha Levy (Bob Barrett) after staff shortages cause the AAU ward to descend into complete chaos.
Potts, meanwhile, will portray senior nurse Eddi McKee, who arrives at Holby on the same day as Chantelle as she accompanies a road traffic accident patient. When she witnesses the disorganisation around her, Eddi convinces Sacha to give her a job too.
From left to right: Sarah-Jane Potts as Eddi McKee, Bob Barrett as Sacha Levy and Lauren Drummond as Chantelle Lane.
Speaking of her new role as Chantelle, Drummond commented: "I'm very excited to be part of such a successful show and to be working with such a great cast and crew. Chantelle is such a fun character to play and I'm really looking forward to getting stuck into her storylines."
Meanwhile, discussing her character, Potts said: "Eddi is a headstrong, determined woman who doesn't stand for any nonsense and soon whips the AAU ward into shape. Thankfully the cast and crew have been every bit as lovely as their preceding reputation, which is helpful when the new girl is having to take on the mantle of ruling the roost!"
Holby City's executive producer Johnathan Young added: "We're delighted to welcome Sarah Jane and Lauren to Holby City. They've brought a new dynamic to the team with two very different characters in the formidable Eddi and the vivacious Chantelle. We have some fantastic storylines ready for them and I'm excited to see what lies ahead."
Drummond began her TV career at Grange Hill before later joining Heartbeat, Waterloo Road, The Royal and Doctors.
Potts is best known for playing Jo Lipsett in Waterloo Road. She has also appeared in the third film of the Zen series and had roles in Sugar Rush and Casualty.
Chantelle and Eddi's joint first episode will air in June.
> Read our Holby City spoilers and news