The 32-year-old is set to become the main leader of the team, coinciding with the exit of Annemiek van Vleuten.
Spratt joined Mitchelton-Scott in 2012 and her extension is a sure sign of commitment from team owner Gerry Ryan.
“I feel like I am at a point in my career where I am really ready to take on the leadership role," Spratt said.
"It’s going to come with more pressure, but I think I am ready for that. In the chances I have had to be the leader, I have done a good job so it’s the next progression for me.
“It means a lot to stay. I have been here since the start in 2012 and it really has become like a family to me.
"I am always looking for an environment where I am happy, where I am challenged and where I am also progressing, and I feel like I’m hitting my best years in the last couple of years and I really believe this is the best place to continue that.
On Spratt's extension, Ryan said she was the "perfect representative" for Mitchelton-Scott.
“Amanda is one of the inaugural members of GreenEDGE Cycling and her contribution to the team, both on and off the bike, is unparalleled," Ryan said.
"She is the perfect representative of who we are and what we are about.
“The past two years, in particular, Amanda has shown she can match it with the best – world championship medals don’t come easily – and we’re confident that our additional support and faith in her at the biggest races over the coming two years will be thoroughly rewarded.”
Spratt, who requested greater responsibility with Mitchelton-Scott, will lead the line for the women's WorldTour team and should revel in more leadership opportunities as she continues to strive for impressive results.
