The 60-year-old guitarist and songwriter said he plans to submit his thesis, "Radial Velocities in the Zodiacal Dust Cloud," to supervisors at Imperial College London within the next two weeks.
Queen were one of Britain's biggest music groups in the 1970s, with hits including "Bohemian Rhapsody" and "We Will Rock You."
After Mercury's death in 1991, May recorded several solo albums, including 1998's "Another World." But his interest in astronomy continued, and he co-wrote "Bang! The Complete History of the Universe," which was published last year.
He was due to finish carrying out astronomical observations at an observatory on the island of La Palma, in Spain's Canary Islands, on Tuesday, the observatory said.
May told the British Broadcasting Corp. that he had always wanted to complete his degree.
"It was unfinished business," he said. "I didn't want an honorary Ph.D. I wanted the real thing that I worked for."