Lord Purvis of Tweed said the current status quo was "horrendous" and demanded action from Scottish authorities.
In 2010 the director of public prosecutions (DPP) in England and Wales issued guidelines making clear that someone acting compassionately to help a terminally ill patient who clearly wished to die was unlikely to face court.
But Lord Purvis, who as a LibDem MSP brought a bill on the issue at Holyrood, said no such guidance has been issued in Scotland.
The state of affairs had continued, he said, despite his repeated calls for action.
"This is a horrendous status quo and Scottish authorities need to act to remedy it," he told members of the House of Lords during a debate on assisted suicide.
Labour's Lord Dubs also agreed with Lord Purvis that "people should have the right to choose to be free from intolerable pain and discomfort - providing it is their free choice".
But other members of the Lords disagreed.
Tory Baroness Morris of Bolton said: "I completely understand the honourable intentions of those who support a change in the law to licence assisted dying. But in reality this means licensing doctors to involve themselves in deliberately bringing about the deaths of some of their patients."
Independent MSP Margo MacDonald has launched a new bill in the Scottish Parliament designed to allow the practice in Scotland.
Under her proposals, trained and licensed facilitators would help patients take the steps necessary to comply with the law and fulfil their wish to die.
Ms MacDonald's first assisted-dying bill was defeated at Holyrood in 2010 by 85 votes to 16. Key to that bill had been the assistance of a physician.
Following the publication of the director of public prosecutions' guidance three years ago, the then Lord Advocate Elish Angiolini, QC, said similar guidance would not be issued in Scotland.
Last night a spokesman for the Crown Office said any action on the issue would not come from the Lord Advocate and was the responsibility of MSPs.
He said: "Any case where someone has helped someone travel abroad to end their life would be considered in terms of its own facts and circumstances in line with the COPFS Prosecution Code.
"Any change in the law in this matter is properly a matter for the Scottish Parliament."