Ian Blackford helped steer the SNP Westminster group to electoral success but his time at the top was not without its bumps along the road.
He built up a reputation for standing up to Conservative Party leaders over the past five years – pushing hard for Boris Johnson to resign.
The SNP politician has been credited with helping recover the ground lost in 2017 when 21 of the party’s MPs lost their seat to pro-union candidates.
The party went on to win a landslide victory in the 2019 general election, with an increased shared of the vote and 13 additional MPs.
Despite bold claims he would be the MP to lead the SNP group right up to independence, the politician is quitting the role.
Dundee-born MP Stephen Flynn was immediately tipped to lead the group at Westminster.
Here are some of the most memorable moments from Mr Blackford’s time in charge.
‘Humble crofter’
The SNP parliamentarian faced frequent jibes after describing himself in the Commons as a “simple crofter with 10 acres”.
He and wife Ann moved to Skye in 2004 and purchased a croft which had “historic links” to her family.
Yet the Edinburgh-born MP has a 20-year career in finance, working as an investment banker.
He eventually led Deutsche Bank operations in Holland and Scotland.
Boris Johnson would go on to mock the SNP’s Westminster leader’s claim during his Tory conference speech in October last year.
He referred to him as a “humble crofter” to the audience in Manchester and in later sparring opportunities in the Commons.
Anger over Grady scandal
Mr Blackford’s leadership came under pressure earlier this year over his handling of sexual misconduct allegations against SNP MP Patrick Grady.
He was criticised for not forcing Mr Grady to step down as the party’s chief whip when accusations against him first emerged.
In a leaked recording, Mr Blackford urged MPs to offer “full support” to their colleague and said he looked forward to welcoming him back.
He apologised for the mishandling of the scandal, admitting Mr Grady’s behaviour was “unacceptable”.
The Highland MP faced calls to quit as Westminster leader in the summer after the recording came to light but he would continue to lead the group for another six months.
The fat jibes from Boris
The former prime minister came under fire for mocking Mr Blackford with ‘fat jibes’ on two separate occasions, during heated exchanges at Prime Minister’s Questions.
In March, the former Tory party leader claimed he and the SNP Westminster leader were both a “living testament to the benefits of moderation”.
It came after the SNP parliamentarian claimed the Tories were partying through the cost of living crisis, referencing a London dinner for MPs held by Mr Johnson the previous evening.
Two months earlier, Mr Johnson claimed the senior SNP MP had been “eating more cake than him” in a heated clash over a lockdown birthday party.
Despite the fiery weekly exchanges, the ex-prime minister was keen to highlight the pair “co-operate well”.
Charles Kennedy election campaign
Before getting a chance to lead the group, Mr Blackford first had to get a seat by defeating Liberal Democrat veteran Charles Kennedy in 2015, after two failed attempts.
The ferocious contest was mired in controversy as a result of the social media abuse faced by the late MP in the run-up to the election.
The well-known politician died at his home near Fort William just three weeks after the election, following a long battle with alcoholism.
Mr Blackford stopped short of apologising over allegations that his campaign hounded the late MP.
On hearing of the resignation, Alex Cole-Hamilton, leader of the Scottish Liberal Democrats, said Mr Blackford has “never been fit to lead”.
Sacking of Joanna Cherry
Joanna Cherry, who carried the Home Office and justice brief for the SNP, was removed from the party’s frontbench by Mr Blackford in February last year.
The MP, who campaigns for women’s sex-based rights, has come in for criticism from some within the party over her stance on gender recognition reform.
Writing in the New Statesman, she claimed her belief that “women are adult human females” made her unpopular with some in the SNP.
SNP sources denied she was removed because of her views around this issue and claimed it came in response to “unacceptable behaviour”.
Mr Blackford later denied a failure of leadership over the abuse Ms Cherry has experienced as a parliamentarian and declined to say if he had offered her any support.
Walking out of Commons
The SNP Westminster chief led his MPs from the House of Commons chamber in protest over the lack of time given to the debate on devolution issues connected to Brexit in 2018.
In dramatic scenes, the SNP leader was ejected from the Commons for repeatedly refusing to sit down after his request for an immediate vote on holding a fresh debate was rejected.
Speaking at the time, he said: “This isn’t a stunt, this is about the harsh reality of the British government acting against the interests of the Scottish people and the Scottish government.”
And earlier this year, the Highland MP was ejected from the Commons for accusing Mr Johnson of being a “liar” who misled the House over Downing Street parties during lockdown.
The SNP group will discuss the appointment of a new leader on December 6.