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The laws narrowly cleared the Senate 36 votes to 34 against the government's wishes on Wednesday morning with support from Labor, the Greens and four crossbenchers.
Mr Morrison fears the changes will restart the people-smuggling trade and trigger an influx of asylum-seeker boats.
"My job now is to ensure that the boats don't come," he told reporters at Parliament House.
Mr Morrison denied his trumped-up rhetoric played into the hands of people smugglers.
"I'm standing between people smugglers and bringing a boat to Australia," he said.
The fast-tracked medical transfers law will only apply to refugees and asylum seekers already on Manus Island and Nauru.
However, Mr Morrison argued people smugglers did not deal with the nuance of the "Canberra bubble" but rather the psychology of messaging about "stronger" and "weaker" borders.
"It might be all fine and nice to talk about these nuances here in this courtyard," he said.
"But when you're in a village in Indonesia and someone is selling you a product, there's no protection or truth in advertising for people smugglers."
The prime minister pledged to reverse the laws if the coalition is re-elected at the poll expected in mid-May.
Earlier, Opposition Leader Bill Shorten sought to send his own message to would-be asylum seekers.
"I just say to people trying to put out the welcome mat for people smugglers, the medivac legislation applies for people who are already there, it does not apply to anyone new," he told reporters.
"So if you think that by buying a ticket on an unsafe boat, paying a people smuggler, a criminal syndicate, you'll get a better deal to come to Australia, you're wrong."
The prime minister was repeatedly asked to say the fast-tracked transfers would not apply to new boat arrivals.
"I'm going to be engaged in very clear and direct messaging to anyone who thinks they should get on a boat," Mr Morrison said.
"I'm here and I will stop you."
Under the new laws, the home affairs minister will have 72 hours to make a decision on whether to agree to a medical transfer.
If the minister rejects the medical reasons, the decision may be reviewed by a medical panel, which can recommend it goes ahead.
Then it's up to the minister to reject it on medical grounds again, or national security grounds, or if the person has a substantial criminal record and poses a threat to the Australian community.
Kon Karapanagiotidis from the Asylum Seeker Resource Centre said the government was trying to "whip up hysteria and fear-mongering", ignoring the fact the new laws applied only to the existing cohort of refugees.