Born in Bolton, Senior joined the youth academy of hometown club Bolton Wanderers, the club he grew up supporting.[3] On 31 August 2019, following major financial troubles that had forced the club to utilise youth players, Senior made his first team debut in a 5–0 away loss against Gillingham.[4] He signed his first professional deal with Bolton Wanderers on 15 May 2020, penning a one-year deal.[5] He scored his first goal on 6 October in a 2–1 defeat against Shrewsbury Town in the EFL Trophy.[6]
On 19 May 2021 Bolton revealed he was contracted for the 2021–2022 season.[7]
On 1 October 2021, he joined Ashton United on loan for a month.[8] He made his debut a day later, starting in a 1–0 defeat to Warrington Town.[9] He scored his first goal for Ashton on 9 October, earning a point for them in a 1–1 draw against Gainsborough Trinity.[10] The loan was extended for a month on 3 November.[11] A week later however, Bolton recalled him from his loan[12] and sent him on loan to York City for a month instead.[13] He made his debut a day later, helping York get a clean sheet in a 0–0 draw against Curzon Ashton.[14] He was recalled from the loan on 9 December[15] and started the next Bolton match two days later in a 1–0 loss against Accrington Stanley.[16] On 25 January 2022, he joined Chorley on loan until the end of the season.[17] He made his debut the same day[18] and was named Man of the Match[19] in a 2–2 draw against Fylde.[20] On 3 March, he was recalled from his loan to provide extra defensive competition due to the absence of Gethin Jones.[21] On 3 May the club confirmed that they had offered him a new contract[22] which he signed on 14 June.[23] On 8 November 2022, he joined Telford United on loan for a month.[24] On 13 December, it was extended until 2 January.[25] He impressed during this loan spell, playing a total of 9 times, with Telford wanting to extend it even further — though Bolton instead decided to recall him.[26] Two weeks later, he joined National League side Halifax Town on a month's loan[27] which was later extended for another month[28] and then extended again to the end of the season.[29] On 25 May 2023, he was announced as one of five B Team releases.[30] Two weeks later, it was announced he would join Halifax on a permanent two year contract on 1 July.[31]