The 45 year-old was detained by serious crime detectives on Wednesday on suspicion of murder.
Last night, the PSNI said it had been granted an additional 36 hours to question the suspect.
Lawlor (35) was shot outside a house in Etna Drive at around 11.50 am on April 4.
The suspect has been arrested by detectives from the Serious Crime Major Investigation team and is being questioned at Musgrave Police station.
Lawlor was one of Ireland s most notorious gangland criminals.
He is believed to have been in the Ardoyne area to collect a debt when he was killed.
Lawlor was one of the chief suspects for the barbaric murder and dismemberment of Drogheda teenager Keane Mulready Woods last January as part of the Drogheda feud.