The Astros took two of three in the series, and four of their seven wins this season have come against the Mariners, their new AL West foe. Seattle and Miami are the only teams without a series win this season.
Carter hit a solo shot in the second, Cedeno belted a three-run shot in the fourth and Laird also connected for a three-run drive in Houston's five-run sixth.
Harrell (2-2) allowed a run and six hits in his longest outing of the season.
Laird had three hits and four RBIs, and Robbie Grossman became the first player since Carlos Gonzalez in 2008 to hit two doubles in his major league debut. It's the first time for a Houston player since James Mouton in 1994.
The Mariners closed out a 1-5 road trip. They were outscored 36-8 in the five losses.
Joe Saunders (1-3) had a second straight rough outing, with the Astros getting to him for 11 hits and eight runs - both season highs - in five-plus innings. He has given up 20 hits and 15 runs in his last two starts.
Carter opened the second inning with a drive to the Crawford Boxes in left field to make it 1-0.
Grossman collected his first major league hit on a ground-rule double with one out in the third. Grossman, who grew up in suburban Houston as an Astros fan, was recalled from Triple-A Oklahoma City after Tuesday night's game when Justin Maxwell went on the disabled list with a broken hand.
Carter drew a walk with one out in the fourth before a single by Carlos Corporan. Cedeno then hit a drive to left for his first homer of the season, pushing the lead to 4-0.
Grossman's second double came to start the fifth inning and Houston tacked on another run when Laird doubled with one out.
Harrell retired eight in a row before Dustin Ackley singled with one out in the fifth. But Robert Andino then grounded into a double play.
The Mariners got on the board in the sixth. Endy Chavez and Kyle Seager opened the inning with consecutive singles, and Chavez scored when Kendrys Morales grounded into a double play.
Michael Morse singled before Jose Altuve ended the inning with a slick defensive play. He made a diving catch on a grounder hit by Justin Smoak and flipped over to make the throw to first from a near sitting position.
Smoak hit a solo homer in the ninth inning.
NOTES: Seager has a career-high 13-game hitting streak. ... The Mariners return home on Thursday to open a four-game series against the Angels. Seattle's Brandon Maurer will oppose Garrett Richards. ... Houston travels Boston where Philip Humber will face Red Sox right-hander Clay Buchholz. ... Seattle manager Eric Wedge said before the game that Andino would replace Brendan Ryan as the starting shortstop for now. Ryan is a solid defender, but has struggled on offense with a .143 average and is just 1 for his last 25. ... Seattle OF Michael Saunders, who is on the disabled list with a sprained right shoulder, could go out for a rehabilitation assignment as soon as Friday.