Prince Harry spoke at the event but it is unclear whether he was paid to appear.
It comes after the couple said they would step back as "senior royals" and work to become financially independent.
They intend to split their time between the UK and North America and, from the spring, will no longer be full-time working royals.
They will stop using their HRH titles, no longer carry out royal duties or military appointments and no longer formally represent the Queen.
The New York Post's Page Six, which first reported the story, said the Sussexes were "keynote speakers" as they made their first appearance together since the Queen granted their wish to step back as full-time royals.
CBS News host Gayle King introduced Meghan, who spoke of her love for her husband, before introducing him at 1 Hotel in Miami's South Beach, Page Six reported.
He is said to have talked about his mental health, something he has spoken about many times in the past.
In 2017, the duke revealed he sought counselling after "shutting down" his emotions for almost 20 years following the death of his mother.
In an ITV documentary last year, Prince Harry described his mental health and the way he deals with the pressures of his life as a matter of "constant management".
Prince Harry arrived in Vancouver last month, where his wife Meghan had been staying with their nine-month-old son Archie.
The couple briefly returned to the UK in January following an extended six-week Christmas break on Vancouver Island.
Since the couple announced their desire to become financially independent there has been speculation about how they might make money.
Public speaking, TV production and book deals have been touted as possible income sources for the couple. They also plan to launch a charitable foundation.
Currently, 95% of the couple's income comes from Prince Charles's income from the Duchy of Cornwall, a vast portfolio of property and financial investments, which brought in £21.6m last year.
It is believed the couple will continue to receive money from Prince Harry's father under the new agreement, although it is unclear whether this will come from the Duchy, his personal wealth, or a combination of the two.
However, the Sussexes will stop receiving money from the taxpayer-funded Sovereign Grant, which makes up the other 5% of their income.