MPs communication on Twitter with other MPs may facilitate forming cross-party solidarity networks and provide public micro deliberation but may also be segregated leading to information bubbles and political polarization. That party-based division lines are running through the online communication networks of politicians is a well-established finding in social media studies; however important knowledge gaps have remained on the complexity of Twitter’s multilayered network developments and their interrelatedness with socio-demographic segregation. Here, we integrate the online-network literature with that on the political consequences of the digital architecture of social media platforms to theorize and scrutinize the extent to which and why Twitter following, @-mentioning and retweeting networks among MPs are segregated along party lines and sex, age and ethnicity. Our unique dynamic take allows us to rigorously study network segregation, including feedback mechanisms between Twitter layers, based on descriptive network statistics and SIENA analyses for Dutch MPs at three time points. The findings show that political segregation patterns are strongest within the retweet layer and weakest for @-mentions. The interrelations between the Twitter network layers aggravate party-based segregation over time. MP Twitter networks are not consistently segregated along social dimensions.