The plan did involve loans but was mostly in the form of grants (gifts). As the Wikipedia entry states:
The Marshall Plan [...] consisted of aid both in the form of grants and in the form of loans. Out of the total, 1.2 billion USD were loan-aid.
Since the total economic support the program involved was of \$13 billion in contemporaneous time (roughly \$132 billion in Sept 2017 money), only 10% approx of the aid was in form of loans.
The UK received 385 million USD of its Marshall Plan aid in the form of loans. Unconnected to the Marshall Plan the UK also received direct loans from the US amounting to 4.6 billion USD. The proportion of Marshall Plan loans versus Marshall Plan grants was roughly 15% to 85% for both the UK and France.
The last payment of these loans by the UK government was done in 2006. Apparently, the last payment from the French occured in 1962.
Germany, which up until the 1953 Debt agreement had to work on the assumption that all the Marshall Plan aid was to be repaid, spent its funds very carefully. Payment for Marshall Plan goods, "counterpart funds", were administered by the Reconstruction Credit Institute, which used the funds for loans inside Germany. In the 1953 Debt agreement the amount of Marshall plan aid that Germany was to repay was reduced to less than 1 billion USD. This made the proportion of loans versus grants to Germany similar to that of France and the UK. The final German loan repayment was made in 1971.