The Mobile Intensive Care Ambulance paramedic was assaulted outside a cafe at Reservoir, in Melbourne's north, just after 11am on Thursday.
He was ordering a coffee when he was attacked from behind, leaving him with neck and face wounds, the Victorian Ambulance Union said.
Investigators allege a man got out of a small, red car and stabbed the paramedic before fleeing in the vehicle.
The suspect, a 32-year-old man, was arrested at a nearby property just before 1pm.
He has been taken into custody and is being questioned by detectives.
A member of the public came to the aid of the paramedic, who called for help over the radio.
Police described his injuries as serious but non-life-threatening.
"This is a vile and chilling attack on one of our paramedics and it must never be tolerated," state ambulance union secretary Danny Hill said.
"Any assault or abuse towards our members needs is unacceptable and needs to be met with the full force of the law.
"These events send a shockwave across the whole workforce."
Victoria implemented laws in October 2018 to mandate a six-month jail term for injuring emergency workers, unless there are "special reasons".
The laws were later tightened after James Haberfield, 22, avoided a prison term despite admitting to attacking a paramedic at musical festival while on a cocktail of drugs.
Haberfield was ordered to serve an 18-month community corrections order and undergo treatment for schizophrenia, which he suffered at the time of the attack.
Under the change, if a person's mental state was self-induced from alcohol or drug use they could not rely on the "special reasons" clause.
Attacks on paramedics should never happen, opposition health spokeswoman Georgie Crozier said.
"It just demonstrates how unsafe our community is and how rampant crime in Victoria is," she said.
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