Scottish Labour was said to be in chaos after its education spokesman quit the job just days after taking over.
A string of top Labour figures lost their seats in last month’s landslide election victory for the SNP.
Shadow education secretary Des McNulty was one of those defeated on May 5, and new Edinburgh North MSP Malcolm Chisholm took over in a reshuffle less than 10 days ago.
But he sensationally quit the key post on Tuesday. In a statement, Labour said he “changed his mind.”
His resignation came on the same day that key posts on Holyrood’s committees were handed out and Labour failed to back him for the job he wanted as convener of the parliament’s health committee.
“It was an argument about the health committee,” he said. “Committee chairs should not be in the gift of the party leader but should be voted on by the parliament.”
Mr Chisholm fell out with Labour colleagues in the last session of parliament when he broke ranks over the SNP’s minimum alcohol pricing policy.
The resignation means Ken Macintosh leaves his arts and culture role to take over at education. Former arts minister Patricia Ferguson takes up her old post.
A Labour spokesman said, “Iain Gray asked Malcolm Chisholm to use his experience and ability in the shadow cabinet and he had agreed to do so. He has since reconsidered and changed his mind.”
SNP MSP Jamie Hepburn said Labour was troubled.
“Malcolm Chisholm may have very good reason for his resignation but for Iain Gray this is yet more chaos,” he said.
“Malcolm Chisholm took positions of principle to support the SNP Government over minimum pricing and the compassionate release of Megrahi.
“His resignation suggests Labour are clinging to the negative policies that got them into this mess in the first place.”
Mr Chisholm, who won the Edinburgh Northern and Leith seat with a 595 majority, resigned as Jack McConnell’s communities minister in the last Labour-Liberal Democrat Scottish Executive, after rebelling against the party line on replacing the Trident nuclear missile system.
He was the first minister to resign from Tony Blair’s government, standing down because of cuts to benefits for single parents.
In 2009, Mr Chisholm voted with the SNP Scottish Government in endorsing the decision to free the Lockerbie bomber on compassionate grounds.
SNP members are expected to be appointed to lead eight of 14 committees.
Labour, still the second largest party, is expected to lead four committees, including public audit and health.
The Conservatives are in line to take the top position on the economy, energy and tourism committee.
The Liberal Democrats will not be represented as conveners or deputies.