The duo, who have worked on the ITV1 breakfast show for a decade, are not part of the new editorial team, which is being headed up by Adrian Chiles and Christine Bleakley.
TV reporter Arnold commented: "I am very happy to take a break from getting up every day at the crack of the sparrows cough! Having said that it has been a craic every day for ten years and I very much look forward to the exciting projects ahead."
Writing on Twitter, he added: "I'm leaving GMTV after ten years - still with a glossy barnet and my own teeth! Will pop up on Daybreak so tweet away! You stars!"
Romano said: "I can honestly say that the last ten years at GMTV have been like a rollercoaster... exciting, scary, hilarious and unpredictable. But most of all never dull. Here in LA I have interviewed and got to know some of the world’s biggest stars, in fact I think I've managed to get through all of them!
"But Hollywood has become my home and, given my personal ties here, this is where I need to be at the moment. It is time to start a new chapter and to explore opportunities on both sides of the Atlantic. I wish GMTV all the best in the future and hope that it continues to be the best that it is."
Director of factual, daytime and GMTV Alison Sharman said that the duo have been a "vital part" of GMTV over the last ten years. "I would like to thank them for the great contribution they have made to the show," she said. "I wish them good luck with the new projects they will be taking on."
Earlier today, Kate Garraway was confirmed as the Daybreak entertainment editor.