How does one become a millionaire with low income earning power?

Compounding is your friend. Whatever your income is, you need to live beneath your means, and invest the difference. Getting a second (and in my case a 3rd & 4th) job for extra income at the start with to get your debts under control and to start your investment portfolio can be key, it helped me tremendously - it was tough, it sucked, but financial speaking it was huge I did so.

Remember the Rule of 72, take your rate of return on investments and divide it into 72 and you get the number of years it will take (approximately) to double. Say your 20 and stocks average about an 8 percent return over your life span. Then $1,000 you put away doubles in about 7 years... or $2000 (at 27), $4000 (at 34), $8000 (at 41), $16,000 (at 48), $32,000 (at 55), $64,000 (at 62).

OK so $64,000 is a long way from a million... but that's one $1000 investment at age 20. Do just $1000 a year for until your 30 and your well over half way there... and really couldn't anyone make a $1000 a year with a part time job or a good side hustle?

And we haven't even gotten close to what for most people are their peak earning years. It just takes a little effort and commitment, and a desire to invest for your future.

Save the money.

Doing all the usual advice of accumulation -- spend less than you earn, avoid debt, automate withdrawals to investing - preferring tax free like a matched 401K or IRA, out found money towards savings, and shop wisely. (Yes your best return is the canned goods sale on 1/2 price plus your coupon ...)

And also try to grow your career and earning power to a higher amount, and run some side gigs to increase your income base.

Win it or steal it.

let's say you make $20 K a year, low income

if you didn't spend any of that money but put it into some savings, it would take 50 years to amass a million, actually a little less if the money earns some interest in those 50 yrs

You have to be willing to sacrifice much and save everything you can for years No cell phone, no cable TV, no internet at home, Limited money spent on clothing, no vacations, sparse living conditions (renting a room not an apartment or a house)

You should also work to increase your skills and value to employers and maybe work 2 full time jobs

You have to decide what you are willing to do to meet your goal, and what reaching that goal will mean

Marry someone with high earning power. -- Or-- If you save $350 a month an invest in the stock market and make an 8% annual return, you would have $1 million in 40 years. The key is starting young and being consistent with saving, and making as high an investment return as you can. Save aggressively early. It takes a long time to get to $100,000, but once you do the compound interest becomes a big factor. For example once $100,000 at 8% is 8000/year, which is $666/ month. So you'd be earning almost twice as much as your $350/ month saving target.

Save some money, and use it to purchase assets that yield income. Take that income and purchase additional assets that yield even more income.

save $1 a day for 2750 years

Its not possible.