Lennon, pictured above, who stood in the last contest against Anas Sarwar, failed to secure enough nominations from MPs and MSPs to make it to the next stage of the contest, with the support of only two MPs and two other MSPs.
She returned to Holyrood as an MSP earlier this month following Sarwar’s resignation as leader and as a member of the Scottish Parliament.
In a statement, Lennon said Scottish Labour risks being “stuck in the past” without “meaningful and radical change”.
She said: “We are not listening to all of our members, the wider movement that built us or the millions of Scots who won’t vote for us.
“This leadership contest should have been a wide debate, rooted in courage, humility and the imagination to become a modern political party for workers and working class communities in Scotland.
“Our values mean nothing without vision, conviction and committed action. We must be a party where people can believe in fair work and a healthy planet; where women’s rights and LGBTQ rights are a shared struggle; where engaging in debate about Scotland’s place in the UK and the global community is a strength, not a weakness.”
“Do better, lead with decency and act with courage. Then, and only then, will there be a viable Scottish Labour Party worthy of the support of the people of Scotland.”