Premier Jay Weatherill’s long-standing chief-of-staff Simon Blewett has resigned.

Blewett, 47, has been with with Weatherill since 2006, guiding him through three portfolios and into the Premiership and weathering the storm of the Debelle Royal Commission.

In a surprise move, Weatherill – the leader of Labor’s Left faction – will replace Blewett with Daniel Romeo, a Right faction heavyweight and the chief-of-staff to Deputy Premier John Rau.

When asked about Blewett’s position by InDaily today, Weatherill confirmed he would be leaving.

He paid tribute to Blewett, giving him much of the credit for Labor’s surprising electoral success at the March 15 election.

“Simon designed and built the structure of our Government and managed the relationships which have allowed us to achieve this remarkable victory,” Weatherill told InDaily in a statement.

“Simon is one of the most decent, thoughtful and fiercely intelligent men I have met. He’s a dear friend and I will miss working with him so closely.”

Blewett, who was an industrial lawyer before he entered political service, has been under intense pressure for the past year after the Debelle inquiry criticised his judgement in not informing then education minister Weatherill about the arrest of a western suburbs school worker for the rape of a child in 2012. He faced numerous calls by the Opposition for his sacking, but Weatherill refused.

The report found that Weatherill wasn’t informed of the case, however Blewett, Weatherill’s chief-of-staff, and another adviser were informed via an email from the Education Department.

Commissioner Bruce Debelle concluded: “Mr Blewett’s judgement was sadly at fault”.

Today, Blewett received support from senior Right faction ministers John Rau and Tom Koutsantonis who both said the Debelle inquiry criticisms had not damaged Blewett’s reputation within the party.

Rau, who worked for Blewett’s father, Hawke era minister Neal Blewett, said Simon Blewett had been a crucial part of the Labor Government.

“Simon has been a person who has worked quietly but very effectively,” Rau said.

“He has been a very important person in a very understated way.”

Rau said he would feel the loss of Romeo, but supported his appointment as Weatherill’s chief-of-staff.

“It’s entirely deserved and he’s the right bloke for the job,” Rau said.

Koutsantonis told InDaily that Blewett had played a critical role in Labor’s election victory.

“He’s calm, he’s resolute, he’s an exceptional thinker,” Koutsantonis said. “He’s one of those rare jewels in public life.”

He added that if Blewett wanted to enter politics, he’d be happy to help him put up his election corflutes.

Romeo, who is aligned with the dominant Right union, the Shop, Distributive and Allied Employees Association (the so-called Shoppies), has been Rau’s chief-of-staff since his elevation to the ministry after the 2010 election.

His appointment as Weatherill’s most senior adviser is telling about the Premier’s new-found position of strength in the party.

Rau was seen as one of Weatherill’s keenest rivals for the Premiership as Labor grappled with a succession plan in the dying days of Mike Rann’s leadership.

The Shoppies are the power base of Don Farrell, the outgoing Labor senator whose political career was effectively ended by Weatherill after he threatened to resign if Farrell was preselected for the safe state Labor seat of Napier.

Before working for Rau, Romeo was a ministerial adviser to then Treasurer Kevin Foley.

Disclosure: David Washington was John Rau’s media adviser in 2011/12.