US Congressman Eric Swalwell will resign from Congress, after dropping out of the California governor race following growing pressure over sexual misconduct allegations.

I am deeply sorry to my family, staff, and constituents for mistakes in judgement I've made in my past, the Democrat said in a letter posted on X.

I will fight the serious, false allegation made against me. However, I must take responsibility and ownership for the mistakes I did make.

Four women accused him last week of misconduct ranging from sexual harassment to rape. This comes as Congress opens an ethics inquiry into Swalwell, who was elected to the House of Representatives in 2012 for a district near San Francisco.

Moments after Swalwell's announcement, another congressman facing an ethics inquiry - Texas Republican Tony Gonzales - posted on X that he will file my retirement from office on Tuesday.

Swalwell, a married father of three who frequently criticizes President Donald Trump, has repeatedly denied the allegations against him.

In his resignation letter, Swalwell said it would be wrong for fellow lawmakers to expel him without due process, within days of an allegation being made. However, he recognized it would also be detrimental for him to continue serving amidst these distractions.

Swalwell plans to work with his staff to ensure a smooth transition as Congress returns from recess, with the ethics committee expected to discuss inquiries into both him and Gonzales.

No clear leader has emerged in the California governor's race from the crowded Democratic field. Following Swalwell's resignation, his name will still appear on voter ballots as election officials confirmed it is too late to remove it.