What is the best way to explain to a potential employer why you may have several career changes two years?

I am currently in the final round of interviewing with a large investment bank. What would would be the best way to explain three jobs in 2 years all of which I left by choice for a better opportunity?

Be very careful.
What ever your justification they will wonder if you won't job hop away from them. Loyalty is always a question.
People sometimes take "temp" jobs for very noble reasons. Think out real hard what made them different.
You might want to play the repentent sinner card. Convince them you want to be a long term shining star in their organization and you have grown out of job hopping.

Good Luck!

There you go : just tell it like it is .

You can say your were recruited away from one, and the other two could not offer you the career advancement that you were looking for. You cant use the same excuse for all three just two different ones will work. There is always well it didnt turn out to be what they had stated it would be and you tried to stick it out but felt that you would be wasting your time and theirs by trying to make it work. Good Luck and I have seen way worse work histories.

potential stepping stones the a better job and career which you now are applying for with them....read tips on employment and interviews to help you better on this site

HONESTLY! If you're in the final round, they must not be overly concerned about your frequent job changes, but I'm sure there's still some level of concern. Give them a brief explanation of what it was about each new job that enticed you to leave your existing job. Then make sure you give them the reassurance they're looking for - that you're not going to leave this job any time soon by explaining all the great things about this job that make it your "dream job", aka the one you'll never want to leave!

Remember that at this level of the interview process, you're probably dealing with someone who is very experienced at conducting interviews, and believe me, they know how to spot someone who is dishing them some BS!

Good luck!!