Hezbollah blamed Israel for his death but Israel has denied the accusation.
Little is known publicly about Lakkis, but he was reputedly close to Hezbollah leader Hassan Nasrallah and an expert in weapons manufacturing.
The news comes a day after Hassan Nasrallah said Saudi Arabia was behind last month’s bombings outside the Iranian embassy in Beirut.
Iran is a major backer of Hezbollah, which has sent fighters to Syria to back the government of Bashar al-Assad.
The conflict in Syria has increased sectarian tensions in its smaller neighbour.
A statement issued by Hezbollah on Wednesday said Lakkis was killed as he returned home from work around midnight. The group said Israel had tried to kill him several times previously.
Neighbours at the quiet residential complex where Lakkis lived said that he arrived home alone shortly before midnight and was just getting out of his car in the parking space beneath his apartment block when he was shot several times in the head at close range by attackers apparently lying in wait.
They said two men were seen running away across some waste ground nearby. The neighbours had no idea that he worked for Hezbollah.
The BBC’s Jim Muir in Beirut says the identity of the attackers remains for the time being at least, a mystery, with much more remaining to be known about why he would have been a target for assassination – and by whom.
Israel denied any involvement in the death.
“These automatic accusations are an innate reflex with Hezbollah,” Israeli foreign ministry spokesman Yigal Palmor said. “They don’t need evidence, they don’t need facts. They just blame anything on Israel.”
Hezbollah – or the Party of God – is a powerful political and military organisation in Lebanon made up mainly of Shia Muslims.
It emerged with financial backing from Iran in the early 1980s and began a struggle to drive Israeli troops from Lebanon.
Hezbollah fought a destructive 34-day war with Israel in 2006. The group said that one of Lakkis’s sons had been killed in that conflict.
Dr Ronen Bergman, a writer on military intelligence affairs for Israeli newspaper Yediot Ahronot, told the BBC Lakkis “became known in Hezbollah as the guy in charge of manufacturing sophisticated weaponry, explosives, booby traps, he was a technical guy”.
He added: “Hassan was the leading figure who received Iranian guidance, he studied in Iran the issues of microwarfare, terrorism, counter-terrorism, and he brought this knowledge with him to Hezbollah, so he was one of these channels through which the Iranians gave Hezbollah their assistance.”