Ohuruogu, as is her style, left it incredibly late but somehow overhauled Botswana's defending champion Amantle Montsho in a photo-finish.
Ohuruogu - who was fifth coming into the final bend and fourth into the home strait - dipped over the line following an amazing late surge.
Initially it seemed the Briton had just missed out on gold, but she was awarded the title in a British record time of 49.404 seconds.
Both women had at first been timed at 49.41, but Ohuruogu was rounded down and Montsho posted 49.408.
Russian Antonina Krivoshapka took bronze in 49.78.
Ohuruogu is now the first British woman to win two world titles at these championships, having won gold in Osaka in 2007.
Ohuruogu is a famed championship performer. But she looked to be in real trouble only to finally turn on the burners, as is her trademark, with the line in sight.
Even with 10 metres remaining she was behind Montsho but the 2008 Olympic champion and London 2012 silver medallist desperately dipped for the line to win by four thousandths of a second.
In addition, the Londoner's time erased Kathy Cooke's 29-year old British record.
"I'm just so grateful and I can't believe I've done that, it feels like a dream to me right now, it's just so surreal," Ohuruogu said.
"This is what I've been working for all year, it was so tight on the line but thankfully it came together and I just made it.
"It's been a really hard three days but it means so much to win the world title again.
"I just dipped in time and just got over the line. The national record is the icing on the cake for me, I've wanted that record for so for long and I never stopped believing or trusting I could do it."