What advice would you give to a senior software engineer/developer who is on the fence about transitioning into leadership?

Leave their tech and logic hat behind- it’s a people role and learn how to collaborate, catch and step back.

Do not do it for the badge. You can carry over your individual contributor state quite high in the hierarchy, without getting into people, process, or technology management.

Instead, take a good look of where are you heading, as a human being, and as a professional. Be honest about your strengths and weaknesses. Understand your inclinations. Se where you would want to out your heart to - and go for it.

If that would be leading? Sure. If not? Not a problem either. Better to be a great contributor than a bad leader.

Double-check your motivation. If it's mostly extrinsic, it'll likely not work well. Check in with yourself on what you are willing to give up. You won't be as hands-on in the leadership role, and even less so over time. Ask yourself if you are comfortable not being the smartest person in the room on the technology subject being discussed. And consider if the leadership potential is actual there. E.g. do people follow you, even when they don't have to?

If your curiosity extends beyond code—toward shaping architecture, priorities, and people growth—leadership can be an exponential growth path. The key is to enter intentionally: build empathy, stay technically credible, and measure success by team acceleration, not personal throughput.

Depends on the definition of "leadership". Assuming the engineer has already been a team lead and was good at it, or they made their team more successful then we are looking at technical leadership, ie: architect etc or management leadership, ie: Engineering Manager. If you enjoy working with a set of teams and then doing whatever it takes to remove roadblocks so that they'll succeed then you should probably give it a go, if your management style is to dictate the plan and then your teams have to roll with your decision then you should stay away from any management positions.