The 59-year-old is being held on suspicion of attempted murder following the incident in south London.
The 59-year-old is being held on suspicion of attempted murder and possession of an offensive weapon following the incident in south London.
British Transport Police and Metropolitan Police officers were called to Tulse Hill station just after 6.30pm on Monday after reports of a man with a knife.
A suspect was then tasered on the platform. There were no reported injuries and the incident was not believed to be terror-related.
A video on social media showed a man wielding a machete above his head before he was tasered and fell to the ground.
Photos also showed several police officers surrounding a man who was lying on the floor.
Conor Fortune said he was on a Thameslink train travelling away from central London at Tulse Hill station when he heard a male voice "shouting quite loudly".
The train conductor then told passengers not to get off because there was "a dangerous man on the platform", he said.
Mr Fortune, from southwest London, said: "After several minutes of being sat on the platform, the driver announced that we were being held and she shut the doors as a precaution, and advised nobody to get off as there was 'a dangerous man on the platform'.
:: Any witnesses should contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 478 of 14/01/2019.