[5] After college, Mosqueda worked on health advocacy at nonprofit organizations, including Sea Mar, which assists Latino seniors with their medical insurance, and the Children's Alliance.

[4][5] Mosqueda then became the political campaign director for the Washington State Labor Council, AFL-CIO and sat on the Health Benefit Exchange Board.

[4] In the August primary, she came in first against seven other challengers, earning 31% of the vote, with affordable housing activist Jon Grant also advancing to the general with 26%.

[7][8] Both Mosqueda and Grant ran as progressives, with Mosqueda running as an "insider" and was endorsed by labor unions and the Young Democrats of King County, while Grant was running as an "outsider" and endorsed by the Democratic Socialists of America and Socialist city council member Kshama Sawant.

[17] In her first year on council, Mosqueda passed legislation to protect domestic workers and voted no on repealing the controversial Seattle head tax, which was meant to build affordable housing and pay for homelessness services.

[18] During her first term she also led the push legislation that would give parents access to paid family leave care benefits after the death of a child and if a partner dies during childbirth.

[21] At the end of 2020, Mosqueda and the majority of the council blocked MayorJenny Durkan proposal to increase the SPD budget to cover overtime costs and voted to ensure "out-of-order" layoffs happen in the department.

[35][34][36] In April 2019 it was announced Mosqueda was the first sitting Seattle city councilmember to be pregnant, and she gave birth to a baby girl in October 2019.