A man has been found guilty of bashing another man unconscious outside a southside bar.

An ACT Supreme Court jury on Wednesday took almost five hours to find Mathew Neish guilty of recklessly inflicting grievous bodily harm.

During the trial, Neish admitted to punching the man outside the Soul Bar in Woden in October 2010, leaving the victim with two black eyes and a fractured eye socket.

But Neish, 26, argued he had acted in self-defence.

The court heard the victim had been drinking with his girlfriend at the bar when he went to buy cigarettes about 11pm.

While away, Neish argued with the victim's girlfriend.

When the victim returned, the defendant accosted him, shouting: ''Go sort that bitch out.''

The complainant said he was then punched in the head without warning.

The victim told the court he covered his head with his arms as Neish punched him to the ground with a further five blows.

He said another four blows while on the ground knocked him unconscious.

But the defence argued Neish had struck the complainant in self-defence, after the man grabbed him by the collar and swung an arm.

Neish told the court the pair then stumbled and fell to the ground where they were separated soon after.

Neish was released on bail and will be sentenced at a late date.