On March 29, 2015, Rau signalled the end of his college career, having amassed 164 points in 160 contests, in signing a three-year entry-level contract with the Florida Panthers.

[3] He was then signed to an amateur try-out contract to complete the season in making his professional debut in the American Hockey League with affiliate, the San Antonio Rampage.

[4] After attending the Panthers 2015 training camp, Rau was assigned to being his rookie professional season with new AHL affiliate, the Portland Pirates on September 25, 2015.

[5] In the 2015–16 season, Rau quickly adapted to the pro level, scoring 17 goals in 48 games before he received his first NHL recall to the Panthers on February 19, 2016.

On December 27th, 2024, Rau signed a deal with Kunlun Red Star of the KHL to finish the 2024-25 season.