Ricky Muir says he was placed in a position he would not wish on his "worst enemies" in having to cast the final vote that allowed Scott Morrison's controversial asylum seeker laws to pass through the Senate.

The new laws mean refugee children will no longer be held in detention, although critics claimed Mr Morrison already had powers to release those children.

"I am forced into a corner to decide between a bad decision or a worse decision": AMEP Senator Ricky Muir on casting the final vote that allowed the new asylum seeker laws to pass the Senate. Credit:Alex Ellinghausen

The low-profile senator for the Motoring Enthusiast Party says he was confronted by "a choice between a bad option and a worse option" in agreeing to support legislation critics say dramatically weakens protections to refugees.

Describing the decision as one of the hardest he had ever had to face, he told the Senate he had voted to help end the uncertainty for some 30,000 asylum seekers who arrived before offshore processing and resettlement became entrenched last year.