The CNN/ORC International survey released Monday also indicated that the number of people who say smoking pot is morally wrong has plunged.
Fifty-five percent of those questioned nationally said marijuana should be made legal, with 44% disagreeing.
The CNN/ORC findings are similar to a Gallup poll conducted in October.
According to the CNN poll and numbers from General Social Survey polling, support for legalizing marijuana has steadily soared over the past quarter century - from 16% in 1987 to 26% in 1996, 34% in 2002, and 43% two years ago.
The survey found interesting divides on the issue.
"There are big differences on age, region, party ID, and gender, with senior citizens, Republicans, and Southerners the only major demographic groups who still oppose the legal use of pot," said CNN Polling Director Keating Holland.
Two-thirds of those 18 to 34 said marijuana should be legal, with 64% of those 34 to 49 in agreement.
Half of those 50 to 64 believe marijuana should be legal, but that number dropped to 39% for those age 65 and older.