After the pick-up driver was rescued, villagers blocked the main road east from the Heroines Monument for several hours, angry at the deaths.
Department of Disaster Prevention and Mitigation officials combined with Kusoldharm Foundation workers to protect the man from villagers until police arrived.
The fatal crash, which took Phuket's toll so far in the ''Seven Days of Danger'' campaign to three dead, came about 7.35pm near Baan Yamu in the Paklok district.
Police believe the man, a Muslim who lives in Samkong in Phuket City, was on his way to visit relatives for Songkran New Year.
He failed to see the couple on a poorly-lit section of road and crashed into their motorcycle and sidecar, which police believe did not have a backlight.
The dead have been named as Pairoj Wisetsombut, 55, and Lamyong Dubayak, 45. They are believed to be relatives. One died at the scene, the other is believed to have died soon after in Thalang Hospital.
The couple had been returning home from selling sweet sugar cane at a local market, police said.
The driver of the Toyota pick-up sat for a time in the vehicle ''talking to his mother and father, and asking Allah why he had been fated to kill two people,'' an officer said.
The man was beaten at least once as a crowd of villagers gathered, then given sanctuary in a Kusoldharm Foundation vehicle.
The man had not been drinking but the road was poorly lit in the spot where the crash took place, police said. The pick-up driver was taken to Thalang Police Station.
DDPM officials said today that there had been 23 crashes on Phuket so far in the Songkran holiday road safety campaign, which began on April 11. One man had died in a motorcycle crash in Phuket City.
Eleven people had been admitted to hospitals in Phuket City, four in Kathu and six in Thalang.
Crashes so far had involved 22 motorcycles and one pick-up, the officials said.
Drinking was given as the cause of 33 percent of the crashes, with driving too fast (9.09 percent) bad overtaking (15.15 percent) and poor lighting (12.12 percent) among other causes.