It also means a pay cut. As a minister outside Cabinet, Mr Borrows was paid $226,300 a year. As Deputy Speaker, he will get $189,400 - a drop of $36,900.
There is no precedent for the Deputy Speaker to automatically assume the role when an incumbent Speaker steps down but Mr Borrows would not be drawn on that issue.
The House sits on October 20 at which stage the MPs are sworn in and matters such as his nomination as Deputy Speaker will be made,
While not acknowledging any disappointment at being overlooked for a Cabinet position, Mr Borrows said he would give the job "the best I can".
"No one should ever think they have done it all [in Parliament] and you should always be striving to give your best whatever the role. That's what I'll be doing. But if I had the choice of a job inside Cabinet I would have taken it."
He said Mr Key made it clear he wanted him as Deputy Speaker because he was respected across all parties in Parliament.
Mr Borrows said he was surprised but very pleased with the call he got from the Prime Minister.
"The PM told me that he required a senior member who was well regarded across the House and could work collaboratively with all parties in the Parliament. I'm told I do enjoy a reputation for collaboration and respect in the Parliament. He also told me that in no way should the change be seen as a demotion and that he was grateful for my work as a minister and this role is aligned with the previous one as a minister outside of Cabinet," he said.
When he entered Parliament in 2005, Mr Borrows was appointed the party's police spokesman. From 2008-2011 he chaired the justice and electoral select committee and was also a member of the social services committee.
In his time as minister he had written the youth-crime action plan to chart a course for youth justice matters over the next 10 years, initiated new legislation such as a new Coroners Bill, Courts and Tribunals Enhanced Services Bill, courts modernisation provisions in the Judicature Bill, and introduced fairer provision regarding welfare fraud.
He said he was probably proudest that while he had taken responsibility for youth-justice policy and child and youth offending, New Zealand had seen youth crime drop by a quarter.
While there would be times when he would step into the Speaker's role during question time in the House, his new job would free him up from the ties of ministerial responsibilities.
"While the new role will mean I have to be less politically partisan, a lack of ministerial duties will mean I can spend more time in the Whanganui electorate at a time when we need to concentrate on building growth, jobs, and opportunities for the Wanganui and South Taranaki regions."
He said now was the time for leadership in business, the community, local and central government to "step up and speak with one voice in support of our region" and he was looking forward to lending his support to that objective.