Tommy Sheppard, MP for Edinburgh East, spoke out following fresh calls for the Lords to be reformed by electoral campaigners.
The Electoral Reform Society (ERS) said the present system of replacing hereditary peers when they leave the upper house must end.
The result of the latest hereditary crossbench election will be announced on Wednesday after voting closed at 5pm on Tuesday.
New research by ERS found that its highest, the electorate for hereditary by-elections has been 803 – at its lowest just three people.
Four by-elections have had more candidates than electors, including the only by-election within the Labour group of hereditary peers for which there were 11 candidates and only three voters.
There is only one female hereditary peer listed on the register of future candidates. No female hereditary peer has been admitted to the House of Lords by by-election.
Tommy Sheppard, SNP spokesman on the House of Lords, said: “The ludicrous farce of hereditary peer ‘by-elections’, where a select few aristocrats are given the right by birth to decide who should make our laws, is a democratic outrage.
“This antiquated bastion of privilege highlights exactly why the House of Lords must be scrapped, and replaced with a fully elected second chamber, at the earliest opportunity.
“With over 800 members the House of Lords is second only to the People’s Congress of China in size - wasting huge sums of public money without any democratic accountability to the people. It is well past its sell by date and the UK government must now take long-overdue action.”