The 31-year-old man was arrested this morning and is currently in custody at a south London police station.
Thirty-year-old Dearlove, who was a relationship manager for Duncan Lawrie Private Bank and who was living with his girlfriend in Eltham, died in hospital after being assaulted in Blackheath on Sunday after a night out with friends.
At the moment, it is believed a man approached the group after they had started talking to a group of women while waiting for a pre-booked taxi to arrive. The man who approached the group then assaulted one of Dearlove's friends before striking Dearlove and causing him to collapse.
A post-mortem examination has provisionally given Dearlove's cause of death as a brain haemorrhage.
"Our investigating is continuing and we've made huge progress in identifying key witnesses and recovering vital CCTV," said detective chief inspector Lee Watling, who is leading the investigation. "However, if you were in the area that night and saw something that may help our investigation but haven't yet spoken to us then please call the Incident Room."
The Incident Room can be reached on 020 8721 4205, although those who wish to remain anonymous can call Crimestoppers on 0800 555 111.
Dearlove also worked at Coutts and Barclays over the course of his career.