The shooting happened at around 9.30pm at an area known as Beary's Cross, on the main Tipperary road outside Limerick city.
The 24-year-old Danny Fitzgerald was shot a number of times beside a caravan located close to a cottage, which he was believed to be renovating.
Three women and a man were arrested when a house close to the scene was searched a short time after the shooting.
A second man was arrested earlier this afternoon, and two further arrests have since been made, meaning a total of four men and three women are now being questioned.
The area where the shooting happened has been sealed off and gardaí from the technical bureau will examine the scene later today.
Gardaí say they are keeping an open mind about the motive for the killing.
They are appealing for witnesses and for information from anyone who may have seen anything suspicious in the area.
