Labour MSP Gordon Jackson has promised to give up legal work and concentrate fully on his role in the Scottish Parliament - and in his constituency.
The QC said he would focus full-time on politics
Mr Jackson provided a written guarantee after his local party warned him he could not do both jobs.
The Glasgow Govan MSP's record was discussed at a meeting of Scottish Labour's executive on Saturday morning.
Mr Jackson was warned by the party's ruling body that if he goes back on his promise, swift action will follow.
He told BBC Scotland: "It wasn't a recent decision. I wrote a letter months ago saying that was my intention.
"There are elections coming up, there are things to do and that's what I wanted to concentrate on.
"I don't think there was ever any problem with constituency work. Sometimes the parliament was difficult because of timetabling, so that difficulty will disappear."
Mr Jackson said he had been involved in the legal profession for about 40 years and insisted he was "more than happy just to do other things".
"Obviously for anyone who makes a commitment, people will watch and see that it's kept," he said.
"My work's in the public domain so it will become obvious what I'm doing."
Nicola Sturgeon described Mr Jackson's pledge as "laughable"
The highly-paid QC announced last December that he would give up his job as a lawyer to concentrate full-time on his Holyrood duties.
It followed an exchange of letters with the party's chief whip, who was reported to have been unhappy about his dual role.
Mr Jackson, who has been an MSP since 1999, had previously indicated that he would be giving up his legal career - but kept working.
He said in May 2001 that he would quit after the High Court questioned his absence while he was in Holyrood.
The SNP's Holyrood leader Nicola Sturgeon, who will fight Mr Jackson's seat in 2007, dismissed the pledge as "laughable".
She said: "We have been here lots of times before and every time he has broken his promise.
"Gordon Jackson is a part-time MSP and next year the SNP intend to give him lots more time to devote to his legal career."
The lawyer earns about £240,000 in legal aid fees on top of his MSP's salary of £50,300.
His habit of rushing from court to the 1700 GMT vote at Holyrood earned him the nickname Crackerjack, after the children's TV programme which began "It's Friday, it's five to five..."