The former "Smash" star and Foster became engaged last year (18) and are looking to wed "sooner than later", according to sources.
"She really wants to get married and doesn't want to wait," one insider tells the New York Post's Page Six.
The couple also wants to have a very intimate wedding.
The ceremony news comes a month after 34-year-old McPhee slammed an online troll for labelling her 69-year-old fiance her "geriatric love".
"Is anyone else totally disturbed by @katharinemcphee and her geriatric love? #daddyissues," the Twitter user wrote.
"oh i LOVE that demi lovato (sic) song!," McPhee responded last month (January 19). "Daddy Issues" is a song from Demi Lovato's 2017 album, "Tell Me You Love Me".
oh i LOVE that demi lovato song! https://t.co/uGCWfJ5eWR— Kat McPhee (@katharinemcphee) January 17, 2019
Katharine also gave fans a sneak peek into her wedding planning process last month (January 2019), after posting her dress shopping trip with her future stepdaughter-in-law Jordan Foster on social media.
"Wedding dress fittings today with @jordiefos! It was such a happy day," she captioned a photo of herself on Instagram wearing a white strappy, backless, floor-length design, complete with a long veil.
However, she later revealed she had not broken the tradition of not letting her groom-to-be see her dress before the wedding by confirming the gown was not the one she'll be wearing on her big day.
This won't be the couple's first trip down the aisle. McPhee was previously married to Nick Cokas from 2008 to 2016, while David has four ex-wives. He split from his fourth wife, former model Yolanda Hadid - the mother of runway beauties Gigi Hadid and Bella Hadid, in late 2015.
McPhee is currently in London starring in musical "Waitress" on the West End stage.