Ruffini edged out Alex Meyer of the United States and compatriot Matteo Furlan for the title after first overcoming a stomach complaint.
But even that challenge was nothing compared to the nerves needed to unfurl a hastily-written proposal convincing Italian teammate Aurora Ponsele to marry him just as he received his medal.
Ponsele signalled back with two fingers shaped in a heart to the delight of watching fans.
"I'm happy for the gold medal and even happier that the answer to my marriage proposal to Aurora (Ponsele) was a sign of love from her," said the champion.
"This was the best moment of my life. Of course I am looking forward to the Olympic Games, but today I understand the meaning of my life".
Ruffini took gold in four hours 53 minutes 10.7 seconds at Kazan's Kazanka venue with Meyer winning silver at just 4.4sec back.
Having finished fourth in the event two years ago in Barcelona, the 27-year-old American finally made it onto the podium.
Furlan claimed third after finishing one min 27.3sec back and won his second bronze at these world championships after a podium place in the 5km earlier this week.
In the women's event, Brazil's Ana Marcela Cunha took gold over the 25km distance with a winning time of 5:13.47.3 hrs with Hungary's Anna Olasz second at 26.3 seconds back.
Germany's Angela Maurer, who won a silver in the event at the 2013 championships, had to settle for bronze this time as she finished 1 min 20.3 sec behind.
Italy's Ruffini wins gold and girlfriend's hand
1 August 2015
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Simone Ruffini proposing to his girlfriend on the podium. Photo: Roman Kruchinin / AFP
1 August 2015
Italy's Simone Ruffini won the world championship men's marathon 25km open water gold medal on Saturday and celebrated by proposing to his girlfriend on the podium.