Yes of course you can! It is not get rich quick scheme as it requires hard work, consistency and providing value to clients. I have hired hundreds of freelancers and worked thousands on hours myself via Upwork.
I think one key element to success is finding what you are passioned about, become an expert in the niche and then bidding projects that match your ideal client and project. By positioning yourself as an expert in your chose niche, you are able charge a much higher rate from clients, but you must do the work to earn the status too.
On Fiverr, I actually just hired a Fiverr provider with whopping 18,000 5* reviews! That is what I call a successful online business.