The striker arrives from Nacional de Montevideo.
"Playing for Roma is a dream I hope to experience very soon," he told the official club Facebook page.
"Thank you to all the Roma fans."
Lopez was accompanied by parents Alejandro and Monica, his brother Mauricio and agent Pablo Bentancur.
"Nico Lopez arrived this afternoon to visit the training ground of AS Roma ahead of formalising the agreement that in future could allow him to play with the Giallorossi jersey," read the statement.