Dassey, who was 16 at the time he gave his confession, was sentenced to life in prison in 2007 for the Halloween 2005 murder of photographer Teresa Halbach.
November 5, 2005: Halbach's cousins find her vehicle under brush and auto parts in the Avery salvage yard.
Last year, a federal magistrate judge ruled that investigators took advantage of Dassey's youth and cognitive problems.
"By the time of the trial, Dassey had recanted his confession, and the State had failed to find any evidence linking him to the crime, but he was convicted and sentenced to life in prison nonetheless".
Dassey's attorneys say they're elated and will take immediate steps to secure his release.
"As of today, Brendan has been locked up for 4,132 days", one of his attorneys, Laura Nirider, told USA TODAY NETWORK-Wisconsin.
Writing the 7th Circuit's majority opinion was Judge William Duffin, who described the confession as "involuntary" based on several factors.
Attorneys for a Wisconsin inmate featured in the Netflix series "Making a Murderer" have petitioned for his release now that a federal appeals court has ruled that his confession was coerced. If they don't do either of those things in the next 90 days, then Dassey could be released from prison. "The pattern of questions demonstrates that the message the investigators conveyed is that the "truth" was what they wanted to hear", reads the decision.
Their cases gained national attention in 2015 when Netflix streamed "Making a Murderer", a multi-part documentary looking at Halbach's death, the ensuing investigation and the trials.
Dassey's uncle, Steven Avery, is in the process of appealing his own conviction.
Lawyers have vowed to fight to free Dassey, whose case garnered global attention after featuring in the popular Netflix series.
The ruling stated that prosecutors' case against Dassey in the original trial rested nearly entirely on Dassey's interviews with police and one phone call with his mother - but no physical evidence.
The ruling came after Dassey's appeal was rejected by state courts.
"But it's clearly the correct decision as the court pointed out the Wisconsin state courts didn't look at the specific qualities of Brendan Dassey: his intellectual limitations, and the specifics about him and they totally missed that analysis".