The incident happened in High Street near Park Parade just before 4.50pm on January 18.
Officers and London Ambulance Service attended and found a man who had been stabbed.
His injuries are deemed neither life-threatening nor life-changing.
A 19-year-old man was arrested shortly after the incident on suspicion of wounding with intent to cause grievous bodily harm.
He remains in police custody.
A Met Police spokesperson said: “On Sunday, 18 January at 04:46hrs police were called to High Street, Harlesden, following reports of a stabbing.
“Met officers attended the scene alongside the London Ambulance Service, who treated a 27-year-old man for stab wounds.
“His injuries have been confirmed as neither life-threatening nor life-changing.
“Officers arrested a 19-year-old man shortly after the incident on suspicion of wounding with intent to cause grievous bodily harm.
“He remains in police custody pending further enquiries.
“If you have any information, please call 101 stating CAD1172/18Jan. You can also call Crimestoppers on 0800 555 111 to remain anonymous.”
