The man's body was left on top of the new billboard until electricity was switched off so workers in a cradle crane could bring the man's body down about 2pm.
Three men were adjusting the electronic billboard when the man was electrocuted. It is believed he came into contact with power lines above the billboard.
The dead worker's body was taken to Vachira Phuket Hospital in Phuket City.
A man climbed a billboard earlier this month at the junction, also known as the Thai Nan Intersection, and threatened to jump.
He climbed down after 90 minutes after being told he would soon be able to talk to his wife.
The contract for work to begin on the 600 million baht underpass on the bypass road at the intersection is due to be signed on October 9 or October 10, Phuket Highways Office Director Samak Luedwonghad confirmed today.
Construction at the intersection - set to take 720 days and involve suggested diversions for Phuket motorists - will take 720 days, he told Phuketwan.