Graham Dwyer is to appeal his murder conviction.
The 42-year-old architect began a mandatory life sentence last month after being found guilty of murdering childcare worker Elaine O'Hara in 2012.
Papers outlining the decision to appeal have now been received by the Courts Service.
The grounds for an appeal have not yet been released, but appeals usually test how safe a conviction is.
The issues that could be contested in this case are how experts extracted text messages which formed the backbone of the case.