The 30-year-old forward joined the Bucks in 2017, playing a role in their promotion to the Northern Premier League in 2021.
Since then, he has scored 29 goals in 83 appearances.
Alongside his time at Bootle, McGowan has featured for Cammell Laird during their time at Step 4.
He will link back up with former Bootle teammates Will Bell, Jay Roberts and Louis Isherwood.
McGowan will go straight into contention as Widnes begin their FA Cup campaign against Emley on Saturday.
Keep up-to-date with our exclusive email newsletters.
Subscribe