In a heartfelt statement on Facebook, Rossum said though she is leaving, "the last eight years have been the best of my life."
"The opportunity to play Fiona has been a gift. There are few characters — female or otherwise — as layered and dynamic. She is a mother lion, fierce, flawed and sexually liberated," she also said. "She is injured, vulnerable, but will never give up. She is living in an economic depression, but refuses to be depressed. She is resourceful. She is loyal. She is brave."
"I knew it the second I read the pilot script, this was different, this was special. I tirelessly prepped the audition with my coach Terry Knickerbocker. I walked to the appointment in the rain so I looked disheveled," Rossum added, recalling when she first took on the role. "During my third audition, when I got the part IN the room, I literally jumped up and down screaming in joyous relief and disbelief."
She also shared how leaving the show is extremely tough because of how tight-knit she has become with the cast and crew.
"See, in real life, unlike Fiona, I'm an only child. I never had a big family," she confessed. "Being ensconced in that messy Gallagher family love is something I'd always dreamed of."
"But even off set, it feels real. We've watched the kids grow up into the strong, talented, independent human beings that they are. I taught Emma to shave her legs," Rossum revealed. "I was there when Ethan learned to drive. Shanola and Jeremy and Joan and Bill danced at my wedding in New York last year."
"Our fearless leader John Wells thankfully held Sam and me up on those rickety chairs during the hora. I've spent the Jewish holy days in temple with David Nevins and his wonderful wife and kids," she went on to say. "It really feels like a family."
In conclusion, Rossum said that she knew the show and fans will
"continue on without" her, but that "there is much more Gallagher story to be told."
"I will always be rooting for my family," she finally said. "Try not to think of me as gone, just think of me as moving down the block."
There is no word at this time on how Rossum's character will be written out of the show, or if there will be a replacement character written in, but with the recent news that former Sons of Anarchy actress Katey Sagal has been added to the shows cast it is possible to surmise that she is could be there to fill that leadership role in some capacity.
Shameless Season 9 premieres Sunday, Sept. 9 at 9 p.m. ET on Showtime.