Merryweather attended Junípero Serra High School in San Mateo, California, where he excelled in baseball.

[9] On October 5, 2018, Merryweather was sent to the Toronto Blue Jays as the player to be named later from the trade that sent Josh Donaldson to Cleveland in August of that year.

[14] With the 2020 Toronto Blue Jays, Merryweather appeared in 13 games, compiling a 0-0 record with 4.15 ERA and 15 strikeouts in 13 innings pitched.

Merryweather was designated for assignment by the Blue Jays on January 10, 2023, after the signing of Brandon Belt became official.

In 2024, Merryweather began the year as part of Chicago's relief corps, posting a 1.93 ERA across 4 contests.

[22] After undergoing additional testing, he was diagnosed with a rib stress fracture in his back,[23] and was transferred to the 60–day injured list on April 17.

On September 19, it was announced that Merryweather would undergo a patellar tendon debridement surgery on his knee, ending his season.