TL;DR: Ninety seconds to two minutes, in three parts: where you are now, the work you have done that is relevant to this job, and why this role. Finish on a specific thing you built, because whatever you end on is what gets asked about next.
How to approach it
Treat it as the one moment you control the agenda rather than as small talk. The mistake is chronology: starting at university and walking forward, which spends the time on the least relevant years and arrives at the present with the interviewer already drifting. Start near the present and connect backwards only where it earns its place.
A strong answer
Three parts, in this order.
Where you are now, in one or two sentences. "I am a systems administrator at a bank, looking after around two hundred Linux servers and the deployment process for our core banking application." Concrete, current, and it tells the interviewer what vocabulary they can use with you.
What you have done that matters for this job. This is most of the answer, and for someone changing fields it is where the work is. Almost everyone moving into DevOps has done DevOps-shaped work without the title. A support engineer has run incidents. A developer has broken a build and fixed a pipeline. A network engineer knows more about the parts that actually fail than most people hired straight into the role. A tester has automated something repetitive. Name the specific thing and give it a number: "I automated our server build with Ansible, which took provisioning from two days of manual steps to about twenty minutes, and removed the configuration differences that were causing half our production incidents."
That sentence does more than any framing of your motivation, because it is evidence.
Why this role, briefly, and forward-looking. One or two sentences, honest and specific to the work rather than the salary. "I want to spend all of my time on the automation and reliability side rather than a fraction of it, and this role is that work at a scale I have not operated at."
Then stop. The most common error after the fear of chronology is going on for six minutes.
For a career change specifically, two things are worth deciding in advance.
Address it directly and briefly. Do not hope nobody notices. One clause is enough: "I have been moving toward this for the last two years, which is why I took the Kubernetes work on our platform team." Avoiding it makes it larger, and defending it at length makes it sound like a weakness you believe in.
Have something you built. A home lab, a personal project, a contribution, anything with a repository and a decision you can explain. For a career changer this is disproportionately powerful, because it converts "wants to do DevOps" into "does DevOps". Being able to say why you chose Terraform over the alternative, and what went wrong, is worth more than a certification.
And on your previous field, treat it as an asset and say how. Someone from finance understands controls and audit. Someone from support understands what an on-call rota costs. Someone from networking already knows the layer most engineers guess at. Naming the transferable thing once is more persuasive than apologising for the background.
What interviewers probe next
"Tell me more about that automation." Which is why you ended on it. Have the detail ready: what it replaced, what broke while you built it, what you would do differently.
"Why leave your current role?" Forward, never backward. What you want to do more of, not what you dislike. Criticising a current employer reads as a preview.
"What do you know about us?" Expected, and answerable in one minute of preparation. What the product does, roughly what the stack looks like from their engineering blog or job posting, and one specific thing you would want to ask about.
Common mistakes
Starting at graduation and walking forward chronologically, which spends the time on the least relevant part.
Listing tools with no outcome. "I have worked with Docker, Kubernetes, Jenkins, Terraform and Ansible" is a keyword list, and the follow-up will find out how deep it goes.
Running long. Two minutes. Rehearse it aloud once, with a timer, because it is always longer than it feels.
Apologising for the career change, or hiding it. One clause, then move on to the evidence.