The 21-year-old Visma Lease-a-bike rider edged out Jordi Meeus and Magnus Cort in a bunch sprint to win the 17th stage of the Grand Tour in Seville.
In doing so, Brennan became the youngest-ever rider to reach five Grand Tour victories and also the first man to win five stages of the same Grand Tour since Marcel Kittel during the 2017 Tour de France.
Just like he did after winning stage 16 on Tuesday, the Brit raised his hands in the air as he crossed the finish line but this time with all five fingers up to mark his fifth stage win of the race.
The largely flat 185km route from Dos Hermanas to Seville was always expected to favour the sprinters.
Spain's Sinuhe Fernandez and France's Enzo Paleni broke away early and created a gap of more than five minutes on the peloton at the halfway point.
Groupama FDJ-United rider Paleni then dropped Fernandez but was caught by the peloton with just three kilometres remaining.
Brennan came around Cort in the closing metres before holding off Meeus to seal another impressive victory in a dramatic finish.
In the general classification, Spain's Enric Mas, eyeing a first Grand Tour victory, maintained his lead over Felix Gall, with four-time Vuelta winner Primoz Roglic in third place.
Stage 18 on Thursday is a 32.1km individual time trial, offering one of the last opportunities for Mas' rivals to reduce their gap to the leader.
