Carroll has had an unimpressive start to the season, leading many to suggest Liverpool had wasted the £35million they spent to bring him to Anfield in January.
However, the England international finally notched his first goal of the campaign in Saturday's 2-0 derby victory over Everton, and Downing believes Carroll's goal could be the catalyst for great things to follow.
"Andy's off the mark now," Downing said, according to The Sun.
"Without scoring, he's been doing well for us and he deserved it for his all-round play."
Downing did admit netting a goal in the Merseyside derby did have extra significance for Carroll.
"That goal is a real bonus and for it to happen in the derby is extra special for him.
"Andy is a quality striker and I'm sure he'll build on this. It was such an important goal as this was a big win for us."
Since joining from Newcastle in January, Carroll has made 14 league appearances for the Reds, scoring three goals in the process.