Viewed as a future leader, Conall McDevitt was the voice of a new generation of SDLP voters.
The Dublin-born politician, who grew up in Spain, was dubbed by some opponents as "the mouth from the south" because of his forthright manner.
He never shied away from heated exchanges in the Assembly and, in March this year, the 41-year-old father-of-three received a death threat from loyalist paramilitaries over his stance on a controversial vote linked to the removal of the Union flag from Belfast City Hall.
His political career began as director of communications for the SDLP from 1996 to 1999 - a time which included the negotiations running up to the Good Friday Agreement and subsequent referendum. He later served as a special adviser in the first power-sharing executive to former agriculture minister Brid Rodgers.
In 2010 he was co-opted to the SDLP Assembly team to replace the long-serving Carmel Hanna and beat all the odds to return a second south Belfast seat for the party at elections the following May.
Just months after his re-election Mr McDevitt, who was regarded as an articulate and capable politician, ran for the leadership of his party and enjoyed some high- profile backing. He lost out to veteran Assemblyman Dr Alistair McDonnell, who also represents south Belfast, and, as a result, relations between the pair were often strained.
The keen cyclist was appointed SDLP health spokesman and at Stormont he was an active member of a number of high-profile scrutiny committees including health and justice. He was also a vocal member of the Northern Ireland Policing Board which holds the Police Service of Northern Ireland to account.
At times Mr McDevitt, who was perceived as an ambitious young moderniser, also endured a turbulent relationship with some of the older party faithful.
His efforts to appeal to the younger voters included embracing social media and he was one of the Assembly's most prolific Twitter users. Indeed, just seconds after his resignation hit the headlines his profile was updated.
"I have resigned as an MLA. It's been a great honour to serve the SDLP and people of S Belfast," he wrote.
His regular political blog, O'Conall Street, also proved popular.
Mr McDevitt's shock departure from public life received a mixed reaction from the online community.
Sinn Fein Deputy First Minister Martin McGuinness was among those who took to Twitter to voice an opinion.
He said: "Conall McDevitt's resignation from Politics today is sad for him & his family & i wish them all the best in the future."
The resignation means the SDLP will have to find a replacement for the South Belfast constituency and leaves a vacancy on their talks team which is due to meet US diplomat Richard Haass later this month to discuss contentious issues such as flags, emblems and dealing with the past.