Felix Jones was man of the match after an excellent display with the full-back assured under the high ball and making yards nearly every time he was in possession.
Earls started well with a big hit early on but it was a lacklustre opening by the province and Kiwi out-half Mat Berquist kicked Treviso into a 2nd minute lead after a Munster infringement at the breakdown.
The unfortunate John Ryan had to be replaced by Stephen Archer in the 8th minute as the home side struggled to put Treviso under any pressure and JJ Hanrahan uncharacteristically missed two kickable penalties midway through the half.
Casey Laulala nearly created the first try when he chipped through a gap on the Treviso left but Italian international full-back Angelo Esposito was well positioned and managed to reach the ball before the chasing Earls.
Berquist missed a difficult penalty from the right on 32 minutes as the visitors threatened to push further in front.
Munster took the lead for the first time on 36 minutes when Hanrahan made a great break through the middle of the Treviso defence before passing inside to Earls who showed great feet to take it past Ludovico Nitoglia and dive in under the posts. Referee Leighton Hodges went to the TMO as Hanrahan's pass looked forward but it was ruled flat and Hanrahan added the easy conversion to make it 7-3.
Berquist had the chance to narrow the gap just before the break but his penalty from the left just faded away and Munster went in at half-time with a four point lead.
Three of Munster's Six Nations heroes, Paul O'Connell, Conor Murray and Tommy O'Donnell, proudly paraded the Six Nations trophy at half-time. O'Connell was a late withdrawal from the side to face Treviso with a slight shoulder niggle.
Rob Penney's side started the second half keen to make amends for a pedestrian first half display and went for the jugular early on with Hanrahan kicking a 42nd minute penalty into the corner.
The resulting rolling maul was halted just short of the line and when Munster went in-field the ball was held up over the line with Hodges awarding the scrum to Munster.
There were a number of resets and Treviso hooker Giovanni Maistri was sin-binned for his part but from the following scrum, with the Munster pack dominant, Treviso were awarded the penalty.
Munster kept up the pressure and were finally rewarded for their dominance in the 55th minute when Downey touched down in the left corner after Hanrahan's cut-out pass. The TMO was called into action once again to check the grounding of the ball but the try was given and Hanrahan brilliantly kicked the touchline conversion to move Munster into a 14-3 lead.
They were unable to build on that advantage as the rain began to pelt down and Treviso centre Michele Campagnaro wasted a great chance when he dropped the ball on the right wing after a turnover on the '22'.
The bench was emptied in the final quarter but with conditions worsening there were no further chances for either side as Munster secured their 14th win in 17 PRO12 games so far this season.
Munster: Felix Jones; Keith Earls, Casey Laulala (Simon Zebo 60), James Downey, Johne Murphy; JJ Hanrahan (Ian Keatley 65), Duncan Williams (Gerry Hurley 74); James Cronin (Dave Kilcoyne 55), Damien Varley (Capt.) (Quentin MacDonald 74), John Ryan (Stephen Archer 7); Dave Foley, Billy Holland (Donncha O'Callaghan 55); Donnacha Ryan, Sean Dougall (CJ Stander 66), Paddy Butler. Replacements: Quentin MacDonald, Dave Kilcoyne, Stephen Archer, Donncha O'Callaghan, CJ Stander, Gerry Hurley, Ian Keatley, Simon Zebo.
Treviso: Angelo Esposito; Christian Loamanu, Michele Campagnaro, Alberto Sgarbi, Ludovico Nitoglia (Leonardo Ghiraldini 50-); Mat Berquist, Edoardo Gori; Alberto De Marchi, Giovanni Maistri, Lorenzo Cittadini; Antonio Pavanello (Capt), Valerio Bernabò; Manoa Vosawai, Marco Filippucci, Robert Barbieri. Replacements: Leonardo Ghiraldini, Matteo Muccignat, Ignacio Fernandez-Rouyet, Marco Fuser, Corniel Van Zyl, Luke McLean, Tobias Botes, James Ambrosini.