During an offseason where the primary question on the lips of Ravens fans is who is going to step up in the passing game, Smith's solid play has made him the primary candidate to be the fourth receiver.
In each Organized Team Activity (OTA), Smith seemed to make at least one eye-opening play immersed within a strong collective body of work.
And "work" is the operative word. Entering his second year in the NFL, Smith has realized that the only way to become a regular contributor on offense is to outwork his teammates.
"Comparing to a year ago, it's night and day," Harbaugh said of the former fourth-round draft pick. "We talk to our guys about making the most progress between their first and second year, but Marcus just goes to work.
"The thing about Marcus is, you see a little bit of improvement every day because he works as hard, or harder, than anybody on the team every single day. So, you start adding all of that stuff up and you watch him out here at practice and you guys are like, 'Wow, this guy is really playing well.'"
The stars seemed to align at the right moment for Smith. He spent most of his rookie campaign on the inactive list or on the sideline. When he did get into a game, Smith generally toiled on special teams.
But towards the end of the year, once Demetrius Williams landed on Injured Reserve with an Achilles' tendon injury, Smith began to get some time from scrimmage.
The Ravens noticed his development then, a program he continued through the following spring.
With Derrick Mason (shoulder), Mark Clayton (foot) and Williams (Achilles) all recovering from injuries, there was Smith running routes with the starters, shagging pinpoint passes from quarterback Joe Flacco.
"I definitely feel that way, be it with the injuries that came along late in the year," Smith said. "Last year I definitely had to take over some of the practice reps and some of the game reps from Derrick and from Mark from them both being hurt. I got a chance to see how this offense works.
"So I feel that now, more mentally than anything else, I've developed by thinking that I can start. I'm not going in there as a third or a fourth receiver."
Harbaugh believes Smith, 6-foot-1, 215 pounds, can eventually increase his standing on the receiving depth chart.
The coach likes Smith's toughness and grit, not to mention his sure hands.
Smith joined the Ravens coming off a stellar senior performance at the University of New Mexico, where he caught a school-record 91 passes for 1,125 yards and four touchdowns.
"We've always thought Marcus was going to be a really good player – he's physical, he's tough and he's a hard worker," Harbaugh noted. "That's a good place to start. He can run – you know he's a former running back – so once he gets the ball in his hands, he's a strong runner North and South.
"I think he's going to be that kind of receiver for us, and I'm excited about Marcus."
Considering that the Ravens have not yet added another wideout via free agency or trade speaks as to how the team feels about Smith and their current crop of receivers.
Smith has worked diligently to ensure that he can earn a prominent role in that group and not be simply known as a special teamer.