New York City is now looking for a contractor to provide the ferries, which began running after the A train was knocked out of service by Superstorm Sandy.
The $2 ride has proven very popular, and it takes just one-third of the time that the subway ride takes.
Service runs from Beach 108th Street and Beach Channel Drive in the Rockaways, then stops at the 58th Street landing in the Brooklyn Army Terminal before continuing to Lower Manhattan and East 34th Street in Midtown.
The extension until May, with an option to extend until August, will allow the city's Economic Development Corporation to issue a request for proposals to determine the viability of long-term service and identify an operator for the line.
"We are committed to the Rockaways' recovery," de Blasio said. "From accelerating rebuilding programs to today's ferry extension, we are going to keep our focus on communities hit hard by Sandy to ensure no one is left behind."
The service, operated by Seastreak, will continue to run on its current schedule and charge $3.50 per ride.
"I applaud the decision of Mayor de Blasio to extend ferry service in the Rockaways," Queens Borough President Melinda Katz said. "Affordable and fast transportation is vital to the growth and future of the peninsula."
This is the fourth extension of the ferry service since its initial launch in November 2012, and roughly 200,000 passengers have taken the trip since.