The Department for Work and Pensions (DWP) has kicked off recruitment for a new chief technology officer (CTO).
The successful applicant will oversee more than £1 billion of annual IT spend for almost 100,000 internal users at 950 sites and will be responsible for over 100 technology architects.
The £135,000-a-year job is described by the department as 'one of the most challenging and rewarding technology roles in the UK today'.
Interested candidates have until January 26 to apply, with final panel interviews due to be conducted during the week beginning March 24.
The CTO will report to the DWP's digital technology director general Mayank Prakash, who started in November 2014. They will also work alongside digital transformation director Kevin Cunnington.
The department is part-way through a digital transformation programme to make its services more customer-centric, develop new services at a faster pace and significantly cut the costs of delivery.
The DWP emphasised the importance of architecture skills and specified it is seeking a candidate with a "track record of transitioning a large enterprise from ageing mainframe technologies to next generation web, social, mobile cloud, Big Data and deep learning technologies".
The department's legacy systems still run on Fujitsu mainframes using the VME operating system installed in 1974.
HM Revenue & Customs CTO Steven Walters has warned these sorts of legacy systems present the biggest challenge to departments in their efforts to become a "fully digital business".
The advert states the appointee will need a "passion to encourage innovation" and a "knack for building partnerships with both technology start-ups and established technology vendors".
They will require hands-on experience in programming, delivering web-based services and APIs, and need to have worked with UNIX or Linux infrastructure, Big Data analytics and data warehouses.
The CTO will be responsible for the IT systems underpinning the delivery of new services such as Personal Independence Payments, the new state pension, and the beleaguered welfare reform project Universal Credit.
The current CTO Jon Ayre joined from consumer electronics firm Philips in August 2013.