The world number one is married to fellow Lithuanian modern pentathlete Andrejus Zadneprovskis, who won bronze in Beijing four years ago and silver in Athens in 2004.
"This is the first Olympic gold medal in our family," said the 28-year-old, who missed the 2010 season to have her son.
"I am immensely excited. I had a great deal of support from the people of Lithuania. It is only a small country. So this means the world to them."
A sport invented by Pierre de Coubertin, founder of the modern Olympics, the one-day event involves fencing, swimming, horse-riding, shooting and running.
Under a complex scoring system, points awarded to athletes in the first three events are combined into a time handicap, with whoever is in the lead getting to start the combined running and shooting event first. The others follow, staggered according to their score.
Asadauskaite won 23 of her 35 fencing bouts to take third position from the start, and despite a disappointing swim which saw her finish seventeenth, she clawed her way to the top of the leaderboard with a solid ride, knocking off just one rail.
That left her starting the nail-biting shoot and run finale - where athletes take five shots at a target before running 1,000m, repeating the procedure three times - side by side with Brazil's Yane Marques after the pair amassed equal points in the first three events.
Despite storming to an early lead after the first shoot, Marques couldn't keep up the pace on the running laps and had to settle for bronze after being overtaken by both the Lithuanian and Britain's Samantha Murray, who snatched the silver on the final 1,000m to a deafening roar from the home crowd.
"I can't put it into words, it was a complete dream to have a home crowd screaming for me and just lift me up, I could have carried on running for another 10 minutes because I was just loving it so much," said Murray.
Modern pentathlon is celebrating its Olympic centenary in London, having made its debut in Stockholm in 1912. But women pentathletes have only been competing since Sydney in 2000.
Latvia's Elena Rublevska, the oldest modern penathlete taking part in London and the only woman to have competed in all four Games since Sydney, led the field after the fencing.
But the 36-year-old couldn't reproduce the kind of form which won her silver at Athens in 2004 and she slowly dropped down the leaderboard to finish eighth.
Hungary's Sarolta Kovacs, who broke the Olympic record in the swimming leg, came in 33rd place after a disastrous ride in which she fell off her horse at the penultimate jump left her near the back of the pack for the start of the shoot and run.
While Beijing gold medalist Lena Schoneborn, who went into the final event in 21st place after a mediocre fence and a poor swim and ride, only managed to claw her way back to 15th.
"It was emotionally exhausting ... after swimming I was in shock and after the riding I just wanted to cry. I didn't feel comfortable with the running and shooting either," said the German. "I'm just relieved that it's over."
That will be a sentiment shared by all 36 of the athletes, who can finally relax and enjoy their Olympic experience after an agonising wait until the final day of the Games to compete.
"I had to make quite a lot of sacrifices in terms of what I have done while at the Olympics so I am looking forward to going (to the closing ceremony) and really embracing fully the atmosphere of the games," said Britain's Murray.
But the celebrations will be short lived for the 22-year-old French and Politics student.
"I have actually got some exams to do in September, so I have got some work to do," she added.