Dieu-Nalio Chery was hit in the jaw by what appeared to be a fragment of one of the bullets fired by Ralph Fethiere.
The Associated Press photographer was treated and released from a Port-au-Prince hospital and was expected to undergo further treatment this week to remove the object from his jaw.
Lauren Easton, AP’s global director of media relations and corporate communications, said: “Thankfully, he is expected to be OK. While it does not appear he was targeted, this is a reminder of the danger journalists around the world face every day while doing their jobs, even on a routine assignment.”
A Senate security guard also suffered what appeared to be a gunshot wound to the stomach.
Senators were convening to approve Fritz William Michel’s nomination as prime minister, when several hundred opposition supporters confronted Mr Fethiere and other senators from the governing party.
He pulled a pistol when protesters rushed at him and members of his entourage.
Moments before the shooting, AP journalists saw supporters of about half a dozen opposition senators approaching Mr Fethiere, hurling dirt at him and accusing him of selling his vote in favour of Mr Michel.
The opposition is trying to block the formation of a new government as a way of pressuring President Jovenel Moise to leave office.
They blame him for failure to address pervasive corruption and mismanaging the economy. The country is running low on fuel and inflation is spiralling, leading to widespread public discontent.
Mr Fethiere told Haitian radio station Signal FM that he opened fire because he feared for his life.
“It was just self-defence,” he said. “Armed individuals tried to attack me. They tried to pull me out of my car and I had to defend myself.”
The vote to ratify Mr Michel was cancelled, the second failed attempt to approve the president’s nominee after his approval by Haiti’s lower house.
The capital was hit by a series of demonstrations and roadblocks on Monday, leading to the latest in a string of near-complete shutdowns of Port-au-Prince that have further damaged the ailing economy.