The youngest child of two university professors, Lorenzo, called Nik, was fondly considered a genius by his family. He started reading at age three and wrote verses too. By the time he was in sixth grade, he was said to have read through all the volumes of Collier's Encyclopedia, aside from becoming totally engrossed in the book, Philippine Society and Revolution, authored by Amado Guerrero, and other sociopolitical writings. Drawing on a prodigious memory, he would discuss all the main battles of the First and Second World Wars. Like his father and one brother, he was proficient in writing essays as well as poems.
When Lansang entered the Philippine Science High School in 1970, his political involvement deepened, especially after joining the Samahang Demokratiko ng Kabataan. With the suspension of the writ of habeas corpus in 1971, he went fulltime into youth and community organizing, living in a very poor section of Tondo in Manila, having been "adopted" into the home of a family there. He left school by his second year.
After the declaration of martial law, when he was 16, Lansang went to join the guerrilla underground in Quezon province. There, for close to three years, he lived among the marginalized farmers and fisherfolk along the Pacific coast, helping them to analyze and find solutions to their problems.
One day in February 1976, Lansang was in a car with five others, bringing rice and food supplies to Quezon from Manila. Apparently, they were being trailed by constabulary forces that caught up with them in Barangay Cagsiay I in Mauban town. Lansang and three of his comrades, one of them a pregnant woman named Leah Masajo, were shot dead and buried in a common grave in Lucena City. He was 19 years old.