Kevin Lau, former editor of the investigative Ming Pao newspaper, was left in a critical condition after Wednesday's brutal attack, seen as highlighting warnings from international watchdogs that the city's media independence is in jeopardy as Beijing seeks tighter control.
Organisers said that 13,000 people including journalists, activists and lawmakers marched in the swiftly organised rally, although police put the turnout lower at 8,600.
Protesters dressed in black waved banners declaring "They can't kill us all" as they condemned the vicious assault on Lau, urging police to solve the case quickly and saying journalists would not be swayed by violence.
"We need to tell the evil power that your knife is not going to deter us," Sham Yee-lan, chairwoman of the Hong Kong Journalists Association told reporters outside the government headquarters, before marching to the city's police department to deliver a petition with 30,000 signatures.
Ronan Chan, a 21-year-old journalism student, told AFP: "I still want to be a journalist. I won't be affected by the incident... A place without freedom of speech is not a civilised society."
Mr Lau's condition improved on Saturday when he was transferred out of an intensive hospital unit to a private ward, greeting journalists with a defiant hand gesture.
A recorded sound clip by Mr Lau played through loudspeakers at the rally declared: "Violence wants us to be afraid. If we are afraid, we will lose freedom. I hope all journalists believe there is justice."
"People should not take freedom for granted. We cannot assume it will never change. It takes everyone to guard it," he was heard to say.
The attack on Mr Lau provoked shock in a city known for its safety, leading Hong Kong's leader, Chief Executive Leung Chun-ying, to stress that freedom of speech will be protected in the financial hub.
But one of Mr Leung's daughters, Leung Chai-yan, sparked an online row after voicing doubt over the attackers' motive, according to the South China Morning Post.
"What does the attack have anything to do with press freedom?! Come on people", she wrote on her Facebook page, drawing criticisms from netizens who accused her of cold blooded comments.
A police investigation into the incident is underway but no arrests have been made so far in what authorities called a "triad-style" attack.
A similar march held the previous week prior to Lau's attack drew 6,000 people protesting at several high-profile incidents seen as aimed at stifling the free press, including the removal of Lau as editor of the liberal Ming Pao, allegedly for being unsympathetic to Beijing. Police put the count for that march at 1,600.
Earlier this month the international Committee to Protect Journalists said media freedom in Hong Kong was "at a low point", citing self-censorship among reporters, financial and physical threats against the media and legislative steps that could hinder investigative reporting.
Paris-based Reporters Without Borders also said in a report that Hong Kong's media independence was "in jeopardy", as China flexes its muscles to stifle critical coverage.
Certain pro-Beijing lawmakers also attended Sunday's rally, local broadcaster Radio Television Hong Kong reported.
Lawmaker Chiang Lai-wan was quoted by the broadcaster as saying that violence against journalists cannot be tolerated regardless of political ideals.