The former Hollyoaks star was cast in the series last year as a new paramedic called Tamzin.
She was initially on the show for three months, but today confirmed via Twitter that she is currently filming new episodes in Cardiff.
Atkinson tweeted: "For those asking, the reason im working in Cardiff now is because ive joined Casualty again. Watch this space for Tamzins return ;) (sic)."
> Read all the latest Casualty news and spoilers
It was reported last year that Atkinson was searching for work in the US.
The actress also revealed in 2011 that she had turned down the chance to return to Hollyoaks on a 12-month contract.