Russia Today London correspondent Sara Firth has left the Kremlin-funded new channel in protest of its coverage of Malaysia Airlines flight MH17.
Firth, who has worked with the channel for five years, described the reporting of Thursday's crash was the "straw that broke the camel's back".
Speaking with the Guardian, Firth said: "It was the most shockingly obvious misinformation and it got to the point where I couldn't defend it any more.
"When this story broke that was the moment I knew I had to go. I walked into the newsroom and there was an eyewitness account making allegations [against Ukraine] and analysis, if you can call it, from our correspondent in the studio.
"It was just appalling, in a situation like that where there are families waiting to be informed and a devastating loss of life."
Firth added that she has always fought against the argument that "RT is an evil network". She contented: "It was not an easy decision, I started my career at RT, and I respect many of the team there.
"In the end it got to the point where I couldn't defend it and I didn't believe there was something to defend. A story like this really highlights it."
Prior to announcing her departure, Firth tweeted: "RT style guide Rule 1: It is ALWAYS *Ukraine's fault (*add name as applicable). Hours later she followed the tweet writing: "I resigned from RT today. I have huge respect for many in the team, but I'm for the truth."
On Thursday, while most media organisations were reporting the flight had been shot down by a suspected Russian-made missile, Russia Today suggested Ukraine was to blame for the crash. One story, which was later toned down, was headlined: 'President Putin's plane might have been the target for Ukrainian missile - sources'.
A statement from Russia Today said the organisation was "not surprised" by Firth's decision adding that the crash was "an absolute terrible tragedy, there are a lot of questions that surround it and everybody is looking for answers."
"Sara has declared that she chooses the truth; apparently we have different definitions of the truth. We believe that the truth is what out reporters see on the ground, with their own eyes and not what's printed in the morning London newspaper," the statement continued.
"In our coverage, RT, unlike the rest of the media, did not draw conclusions before the official investigation has even begun. We show all sides of the story, even if everyone else has already decided which side is to blame."
A total of 298 people were killed in the crash which has dominated press coverage since Thursday, with Hacked Off criticising graphic images and video footage posted on social media during the immediate aftermath of the crash.