The British cyclist faced a four year suspension for three whereabouts failures in the last 12 months.
But the Court of Arbitration for Sport (CAS) agreed with her legal team that procedures weren't followed for the first of the three tests.
A statement made by Armistead's representation said:
"The ruling relates to a UKAD anti-doping test which was asserted to have been attempted on Thursday August 20, 2015, whilst Armitstead was staying at the team hotel, during the UCI Women's Road World Cup in Sweden.
"CAS ruled that the UKAD doping control officer had not followed required procedures nor made reasonable attempts to locate Armitstead,"
"CAS also ruled that there was no negligence on Armitstead's part and that she had followed procedures according to the guidelines."
The error was said to have occurred when the doping official could not locate her room number nor reach her by phone, but she was successfully tested in competition the following day.
The statement said the world champion took responsibility for the other two failures. The second was an administrative failure on 5 October 2015 and the third was a missed test on 9 June 2016 this year following "an emergency change of plans due to a serious illness within her family".
Armitstead said she was notified on 11th July by UK Anti-Doping (UKAD) of her suspension pending disciplinary action. Announced by organisers as a last minute withdrawal from La Course and absent from the RideLondon Classique, her suspension was not made known by UKAD, British Cycling, or Armitstead herself at the time.
The 27-year-old is the hot favourite to win the gold at the Rio Olympics on Sunday.
"I have always been and will always be a clean athlete and have been vocal in my anti-doping stance throughout my career," she said via the statement.
The news of Armitstead's missed tests was revealed by the Daily Mail, which said she was supported by a legal team backed by British Cycling.
"We are satisfied that the matter has now been resolved and look forward to Rio, where we have full confidence that the team will be a great success," a British Cycling spokesman said.