Current managing partner John Mullins will stay on as Chairman of the firm and as a practising senior partner.
The new managing partner will be Curt Schatz, who has been at the firm for over 20 years.
Established in 1980 by Mr Mullins' father Patrick Mullins (Senior), Mullins Lawyers now has 95 staff including 18 partners.
Mr Mullins, who held the managing partner role for the duration of that time, said he was proud of its growth.
"I’ve seen the firm grow from very small to a well respected mid-tier commercial firm," he said.
Partners were informed of Mr Mullins' plans in late January and Mr Schatz was unanimously elected as the new firm head.
"He is a natural leader and has my full support," Mr Mullins said. "I know that Curt will do an excellent job. He is a very driven and competitive person as he has shown by the growth and success of our Property & Hospitality group which he leads.”
He suggested the firm had resisted merger opportunities over the year in a bid to "define our own destiny."
"Defining our own future means we can control the character and the nature of the firm and ensure we maintain the high ethical standards that were so important to my father, my brother Pat, myself and all of our Partners. We know Curt shares these views and that the firm is in good hands," he said.
Mr Schatz called the appointment an honour and said the transition was likely to be smooth.
"From a client perspective, I see my appointment to the Managing Partner role as an opportunity to do even more with the industries the firm and I personally work in," he said. "I have taken several steps to ensure my clients, my team and my referrers are not impacted by the additional responsibilities of the Managing Partner role.”