Mark Munro, 31, and James Robertson, 27, pushed 27-year-old Russell Robertson over bridge railings into the Forth and Clyde Canal.
Mr Robertson, from Falkirk, hit his head on a metal bridge support as he fell and fractured his skull. His body was pulled from the canal more than an hour later.
The High Court in Glasgow heard that he would have been unconscious when he went into the water.
The court heard that all three men had been at the Warehouse nightclub in Falkirk and were making their way home after 3am.
Robertson, from Pitlochry, was approached by the victim and they began fighting before Munro, who had been using his phone, became involved.
Eyewitnessess reported seeing the men apparently “play fighting” before the two accused grabbed Mr Robertson by the legs.
The two tipped Mr Robertson over the edge of Bainsford Bridge, Falkirk, and into the canal before they ran off.
In court, both men blamed each other.
Munro, from Denny, tried to portray himself as a hero who tried to save Mr Robertson, but the jury did not believe him.
Robertson admitted being in an initial struggle, but claimed he was walking away towards Falkirk when the man went into the water.
Both men were on trial accused of murdering Mr Robertson.
They were convicted of the reduced charge of culpable homicide.
Nightclub security manager Kevin Gibney told how he saw Mr Robertson disappear off the bridge as he struggled with the two killers.
Mr Gibney said: “One minute he was there and the next he was gone. The two gentlemen ran across the road.”
Minutes later Mr Gibney picked out Munro and Robertson to police and they were detained and later charged with murder.
Another eyewitness Cameron Binnie, 19, said that he and some friends were waiting at a bus stop near the bridge after a night out at the Warehouse nightclub.
He said it was around 3:20am and they were texting friends and taxi firms trying to get a lift home when he saw three men who he thought were “larking about”.
Mr Binnie said: “It looked like play fighting. One of the men had another man in a headlock. I thought it was pals just mucking about.”
The lifeguard said he changed his mind when he saw the two men grab the other man’s legs.
He added: “I just saw them lifting his legs.”
Judge Lady Carmichael deferred sentence until 23 August at the High Court in Edinburgh for background reports and detained both accused in custody. Defence counsel will give their pleas in mitigation before sentencing.